Reservoir Safety in Wales 2021 - 2023

For the period 1 April 2021 to 31 March 2023

Biennial report to the Minister for Reservoir Safety


We are the enforcement authority for the Reservoirs Act 1975 in Wales and in this biennial report for April 2021 to March 2023, we report to the Welsh Minister on compliance with this law and our work to ensure the safety of reservoirs. Our report is provided in three parts:

  1. Our work as an enforcement authority to secure that reservoir undertakers observe and comply with the law
  2. Our work to discharge our own responsibilities as a reservoir undertaker
  3. Our forward look to the next two years

The number of reservoirs registered and regulated as large raised reservoirs has almost doubled from 224 to 397 since the 2016 amendments reduced the threshold capacity for registration from 25,000 to 10,000 cubic metres.

We have continued to use our power to designate ‘high-risk reservoirs’ where we think an uncontrolled release of water could endanger life. The flood mapping to support this work showed us that the smaller reservoirs can pose a hazard to life, but their generally smaller dimensions mean proportionally fewer are designated than those registered prior to 2016.

Our designations focus our work to ensure the principal requirements of the law are applied. We report the levels of compliance on this as a percentage and the number of reservoirs where we have recorded breaches with each of our key indicators for reservoir safety, as shown below:

Reservoir activity


Number of non-compliant reservoirs

Construction 100% 0
Supervision 94.7% 21
Inspection 99.5% 2
Safety measures 94.0% 24
Maintenance (statutory) 99.7% 2
Monitoring and record keeping 93.7% 25


The overall compliance figures remain high. Most reservoir undertakers are taking their responsibilities seriously and meet the minimum requirements laid down by law. However, the level of compliance has declined across several indicators since our last report. This decline occurs in part because of new and greater visibility of smaller reservoirs brought about by the 2016 Regulations, and a slow response by these ‘new’ undertakers who are unfamiliar with regulation.

More concerning is that compliance has also decreased among undertakers who have been regulated since the law was first introduced. It is notable that publicly funded bodies contribute much of the non-compliance for the implementation of safety measures. Compliance is often achieved but more slowly than required by the statutory timescales imposed, sometimes by years. Achieving 100% compliance across all undertakers is testing yet it remains our clear aim.

Part 2 of our report focusses on our work as a reservoir undertaker for 37 reservoirs used for flood risk management and conservation, and includes those reservoirs located within the Welsh Government Woodland Estate.

We disclose and explain non-compliance at six of our reservoirs, two of which remain extant at the time of publication. This is important work which we do not approach lightly but concede more needs to be done. A comprehensive project is in place to address all the issues with regular oversight by a qualified civil engineer.

In Part 3 we look to the next two years. Our primary focus must be to regain higher levels of compliance, especially at high-risk reservoirs. We seek to bring long-running cases of non-compliance to conclusion. We anticipate a lack of undertakers’ funds as a core block to achieving this, with delays increasing costs further. This also applies to undertakers who are publicly funded. Our aim is to push all public bodies, including NRW, to demonstrate a stronger “must do” approach to these important legal requirements.

The pressures caused by the changing climate and cycles of more intense rainfall and drought are forecast to increase. Reservoirs must be robust under these extreme conditions. Ensuring their integrity and safety is important work that undertakers must complete regardless of financial or other pressures.

We shall continue to engage with stakeholders to improve our regulation and to decide how best to implement changes to address the recommendations made by Professor Balmforth following the 2019 Toddbrook reservoir incident. We have begun work with Welsh Government and our counterparts in England, in projects associated with hazard determination and with post incident reporting. We will continue to contribute to projects which benefit Wales in the medium to long-term and from which we can form the basis of our advice to the Welsh Government.

To enable more frequent analysis and feedback during a time of potential change, we intend to produce future reports to the Welsh Minister annually, covering the same requirements as this biennial report.


Natural Resources Wales is the enforcement authority for the Reservoirs Act 1975 in Wales. We provide this report to discharge our duty as required by section 3 of the Reservoirs Act 1975, to provide this report to the Minister on our activities from 1 April 2021 to 31 March 2023.

Specifically, we must report to the Welsh Minister on:

  • the number of large raised reservoirs that have been registered
  • the steps NRW has taken to ensure the undertakers of large raised reservoirs have complied with the requirements of the 1975 Act


  • the number of large raised reservoirs for which we are the undertakers
  • any steps we have taken to observe and comply with the requirements of the 1975 Act.

It is our duty to ensure reservoir owners and operators comply with the law. Our ultimate purpose is to provide reassurance that the flood risk from reservoirs is well managed.

We have a dual role. As well as being the enforcement authority, we manage and operate a portfolio of reservoirs for flood management and conservation benefits. We also manage reservoirs within the Welsh Government Woodland Estate on behalf of the Welsh Ministers. We separate our report to reflect these different responsibilities.

Reforming the regimes which protect reservoir safety remains an important topic for us. Since the major incident at Toddbrook in 2019, we have continued working with Welsh Government, and with colleagues at the Department for Environment, Food and Rural Affairs (Defra) and the Environment Agency in England to understand how improvements may be made.

In our report, we have tried to illustrate the scale of reservoir management in Wales and the overall performance of reservoir owners and operators. We also report on the challenges faced by owners recently brought into regulation and the cost of meeting new liabilities.

Part 1 - Regulation of the Reservoirs Act 1975

Our principal duty is to ensure reservoir undertakers observe and comply with the Reservoirs Act 1975. This law was last amended in 2016 to improve our knowledge of risks from smaller reservoirs and to make judgment on the level of regulation needed. The legislation sets minimum standards to prevent an uncontrolled release of water from large raised reservoirs. These are reservoirs that can store 10,000 cubic metres of water, or more, above the natural level of the surrounding land including artificially raised lakes.


The total number of registered reservoirs for each biennial reporting period is shown in Table 1 below. The increase in the number of reservoirs follows our work after the 2016 amendments to the Reservoirs Act 1975 which lowered the capacity threshold for registration from 25,000 to 10,000 cubic metres. There are now almost double the number of regulated reservoirs in Wales.

We continue to seek out additional reservoirs which may require registration however we believe these are predominantly ones with lesser volumes and pose a smaller flood risk.

Table 1. The number of registered large raised reservoirs in Wales on 31 March between 2013 and 2023.

Year 2013 2015 2017 2019 2021 2023
Number of registered large, raised reservoirs​ 201 224 316 366 371 397 

Risk designation

The Reservoirs Act 1975 places a duty on us to designate large raised reservoirs as ‘high-risk reservoirs’ if we think an uncontrolled release of water could endanger human life. This is a consequence-based assessment and does not confer any likelihood of failure.

Undertakers for high-risk reservoirs must adhere to all the requirements of the law, most importantly the inspection and supervision elements provided by qualified civil engineers. Lower risk reservoirs do not have this requirement.

We approached the designation of reservoirs in stages. In stage 1 we designated the reservoirs that were registered prior to the 2016 regulations which introduced this requirement. 88% of these reservoirs were designated as high-risk reservoirs, with the remaining 12% shown to pose a sufficiently low hazard and were released from the statutory requirement for inspection by independent engineers.

Stage 2 is our designation of reservoirs registered since 2016. We have reviewed 122 of these 177 smaller reservoirs. 

Table 2. Risk designations completed for reservoirs registered since 2016

Designation Number of reservoirs
High-risk reservoir 77 (44%)
Undesignated (‘not high-risk) 45 (25%)
Undetermined 55 (31%)


Most of the reservoirs which have an undetermined designation were registered after we produced flood maps. Further reservoir flood mapping is needed before we can continue with these remaining designations. We are scheduling a project and request for funding to carry out this mapping during 2024-25. Successful completion of the mapping will mean we are able to designate the remaining reservoirs by 2026.

Prior to designation, there few requirements placed on undertakers. We provide newsletters and guidance to the undertakers so that the principles of reservoir safety are brought to their attention and reinforce their liability for the safety of their reservoir, regardless of its designation.

Following designation as a high-risk reservoir, the undertakers must appoint engineers for specific activities and act on their recommendations. We report on this in more detail below.


The responsibility for complying with the law lies with the reservoir undertakers. The undertakers are the people or organisations who manage and operate the reservoir. In the absence of active reservoir operation, the liability falls to the owners and their lessees.

The law requires undertakers to manage their reservoirs using the guidance and recommendations of qualified civil engineers at specific points in the lifetime of a reservoir. These engineers are appointed to specialist reservoir panels by Government, using advice from the Reservoirs Committee of the Institution of Civil Engineers. When a qualified civil engineer is in place to supervise activity at a reservoir, we are provided with reassurance that a professional view of safety is available where shortfalls can be identified and escalated if needed.

We report on the period 1 April 2021 to 31 March 2023. Table 3 below summarises overall compliance with the Reservoirs Act 1975 in comparison with the previous biennial reporting period ending 31 March 2021.

Table 3. The number of reservoirs non-compliant with the Reservoirs Act 1975.

Reservoir 2019 - 2021 2021 - 2023
Total number of registered reservoirs 371 397
Total number of reservoirs with non-compliance recorded or outstanding 73 73


It is coincidental that the number of non-compliant reservoirs has remained the same; they are not all the same reservoirs.

The most important indicators of reservoir safety are based on the principle of oversight by engineers, and we are responsible for ensuring they are implemented, specifically:

  • the appointment of a construction engineer to design and supervise the construction and alteration of reservoirs
  • the appointment of a supervising engineer for every high-risk reservoir that is not under the supervision of a construction engineer. The supervising engineer provides a written statement on the performance of the reservoir and the undertakers’ actions
  • the appointment of an inspecting engineer for every high-risk reservoir to carry out a periodic inspection. In their report, the inspecting engineer will make recommendations for safety, maintenance, and monitoring
  • certification by an inspecting engineer to confirm the completion of measures to be taken in the interests of safety
  • other activities required of undertakers but not requiring oversight by engineers, such as maintenance, monitoring and record keeping

All statutory reports, statements and certificates are copied to us and retained for reference.

Table 4 below shows the number of reservoirs which we recorded as non-compliant for each of the indicators described above. We have provided the corresponding number of compliant reservoirs as a percentage of the total number of registered reservoirs. The results from the previous reporting period are given for comparison.

Table 4. The number of reservoirs non-compliant with the Reservoirs Act 1975 and resulting percentage of compliance for each key indicator of reservoir safety.

Reservoir activity 2019 - 2021 Percentage 2021 - 2023 Percentage
Construction 0 100% 0 100%
Supervision 2 99.5% 21 94.7%
Inspection 2 99.5% 2 99.5%
Safety measures 11 97.0% 24 94%
Maintenance (statutory) 3 99.2% 2 99.7%
Monitoring and record keeping 15 95.7% 25 93.7%


The decline in compliance since our last report reflects, in part, the increase in the number of undertakers whose reservoirs have been brought into regulation more recently and who are less familiar and less experienced in fulfilling their responsibilities. Some have been unwilling to commit immediately to what is newly required of them.

Our aim is always to achieve 100% compliance across the key indicators. Compliance includes assessment of matters other than the integrity of the dam, for example, surveillance and record keeping. The decline in compliance does not equate to a decline in structural safety but reflects the overall approach to management and operation by the undertaker. There is also greater transparency of previously unknown reservoirs, maintained to no particular standard and rarely visited by a reservoir engineer, if at all. By bringing them into regulation, the risks are now more visible and can be addressed properly.


New construction or alterations

100% compliance

Reservoir failure has historically been linked to inadequate design and poor construction, with failures occuring in the early years of a reservoir’s life. The construction and alteration of reservoirs are controlled activities, and undertakers must appoint a construction engineer to design and supervise the work.

A preliminary certificate is given by the construction engineer when the reservoir is considered safe to fill to a given level.

A final certificate is given after a minimum period of three years to prove the structure and to confirm that the structure is ‘sound and satisfactory’.

During the reporting period we monitored construction activities at 11 reservoirs.

  • Three were certified complete
  • Six remain under a preliminary certificate for first filling
  • Two reservoirs are yet to receive a preliminary certificate

Table 5. Construction and alteration activity during 2021-23, *FSA – Flood Storage Area

Reservoir Nature of activity Engineer appointment Preliminary certificate Final certificate
Llwyn Onn 1 Construction 22/02/2017 04/10/2017 08/02/2023
Llwyn Onn 2 Construction 06/11/2017 10/09/2018 08/02/2023
Surf Snowdonia Construction 02/07/2014 30/09/2019 06/07/2021
Pontarddulais FSA* Construction 04/12/2017 29/01/2021 pending
Rhyl Golf Course FSA* Construction 31/05/2020 02/11/2020 pending
Dolwen Alteration 09/02/2020 22/12/2020 pending
Llyn Mawr Construction 27/09/2018 27/07/2020 pending
Cae Llwyd Alteration 28/10/2021 25/11/2022 pending
Pengarnddu Construction 14/07/2021 15/06/2022 pending
Pendinas Alteration 17/12/2021 pending pending
The British Ironworks Construction 27/02/2023 pending pending


We monitor the timely issue of certificates and seek information from the construction engineer when there appears to be a delay.

We recorded no offences for improper construction or alteration of a reservoir during the reporting period.

First inspection of older constructions

The 2016 amendments brought many reservoirs into regulation which were not constructed under the controls of the previous Reservoirs Act. These reservoirs must be inspected by a construction engineer and a final certificate given. There can be a delay before the issue of a certificate whilst any matters in the interests of safety are addressed. A first inspection has been carried out at the following reservoirs.

Table 6. First construction inspection at older reservoirs

Reservoir Engineer appointment Preliminary certificate Final certificate
Rhyl Golf Course FSA 31/05/2020 02/11/2020 pending
Crai No.2 12/06/2020 Not required 30/07/2021
Duffryn No.1 12/06/2020 Not required pending
Radyr Llanilid 26/06/2020 Not required pending
Ty Canol 09/07/2020 Not required 30/07/2021
Cribbarth No.1 04/09/2020 Not required 30/04/2021
Morriston 02/11/2020 Not required 01/09/2021
Cefnllan 25/11/2020 Not required 03/09/2021
Tongwynlais No.1 16/02/2021 Not required 21/09/2021
Townhill 19/03/2021 Not required 04/02/2022
Llantarnam 25/03/2021 Not required 15/11/2021
Llangeinor 01/04/2021 Not required 07/07/2022
Catsash No.1 28/04/2021 Not required 28/04/2021
Court Colman 05/05/2021 Not required 05/04/2022
Clase 18/05/2021 Not required 04/05/2022
Windmill Hill 08/06/2021 Not required pending
Cockett 10/10/2021 Not required pending
Bolton Hill 18/10/2021 Not required 14/12/2022
Greenhill 07/12/2021 Not required pending
Pen-y-Mynydd 16/02/2022 11/08/2022 pending
Cefn Hirgoed No.1 29/03/2022 Not required 10/02/2023
Bryngwyn New 30/03/2022 Not required 19/01/2023
Canada Lake 04/07/2022 23/12/2022 pending
Bolton Hill Low Level Raw 31/08/2022 Not required 12/12/2022
Festival Lake 21/12/2022 Not required pending


No abandoned reservoirs were brought back into use during this period.


94.7% compliance

After construction and the issue of a final certificate, every reservoir that is designated as a high-risk reservoir, must have a supervising engineer appointed to it at all times. The supervising engineer monitors the reservoir’s behaviour, gives advice to the undertaker, and provides a written statement annually. The supervising engineers’ statements must be copied to us. This appointment is important for us because it reassures us that a qualified civil engineer is visiting and assessing safety at least once every year, with sufficient professionalism to bring any problems to the attention of the undertakers and to us.

We received and processed 106 new supervising engineer appointments for high-risk reservoirs.

Historically, the number of reservoirs without a supervising engineer has been close to zero. However, Table 7 below shows there were 21 occasions where a supervising engineer has not been appointed for a high-risk reservoir. This represents a significant decrease in compliance. We monitor these reservoirs closely and provide regular advice on the requirements. We may serve notice requiring an appointment to be made and can enforce this by appointing an engineer ourselves if the undertakers fail to comply with a notice. Four reservoirs were under notice to appoint a supervising engineer at the close of the reporting period.

Table 7. High-risk reservoirs where a supervising engineer was not appointed in time during 2021-23

Reservoir Undertakers Occurrence Response
Bicton 1 ‘Upper’ (*) Bicton Farms Ltd. 28/06/2022 Under investigation
Bicton 2 ‘Middle’ (*) Bicton Farms Ltd. 28/06/2022 Under investigation
Bicton 3 ‘Lower’ (*) Bicton Farms Ltd. 28/06/2022 Under investigation
Blaen Bran Eurolago e Foresta Ltd. 20/12/2022 Under notice
Butetown Caerphilly CBC 05/10/2022 Warning
Jepson’s Pond Caerphilly CBC 05/10/2022 Warning
Llyn-y-Garnedd (*) Instant Timber Ltd. 12/01/2022 Under investigation
Llywernog Pond (*) Private landowner 13/01/2022 Under investigation
Nant-y-Draenog Eurolago e Foresta Ltd. 20/12/2022 Under Notice
Parc Cwm Darran (*) Caerphilly CBC 25/03/2022 Warning
Penpedairheol FSR Caerphilly CBC 05/10/2022 Warning
Pen-y-Fan Pond Caerphilly CBC 05/10/2022 Warning
Pond Feeder (*) Caerphilly CBC 25/03/2022 Warning
Purge Pond A (*) Uniper UK Ltd. 02/10/2022 Under investigation

Purge Pond B (*)

Uniper UK Ltd. 02/10/2022 Under investigation
Settling Tank (*) Uniper UK Ltd. 02/10/2022 Under investigation
Upper Winsle (*) Private landowner 14/12/2022 Under investigation
Van Pool (*) Private landowner, Powys County Council 14/12/2022 Under investigation
Warren Mill (*) Private landowner 13/01/2022 Under investigation
Waun-y-Pound Middle Fragile Limited 13/01/2022 Under Notice
Waun-y-Pound Upper Fragile Limited 02/09/2022 Under Notice


(*) Reservoir in first year of designation as a high-risk reservoir

We attribute most of the increase in offences where the reservoir has been brought into regulation and recently designated as a high-risk reservoir. This applies to entries marked with an asterisk (*). Warnings and notices have been issued to reservoir undertakers which have been longer standing high-risk reservoirs. We review cases monthly and additional steps to secure the safety of reservoirs or to escalate enforcement are decided with priority given to those where the risk to public safety is highest.

Section 12 statements

Supervising engineers have a duty to provide a written statement for each high-risk reservoir they are appointed to. These statements are sent directly to the undertaker to draw attention to the behaviour of the reservoir and to provide advice. The statements contain updates on progress to deliver the safety measures recommended at the last inspection and provide commentary on the undertakers’ fulfilment of surveillance, maintenance and record keeping. These statements are copied to us. We received and processed 420 statements from which we gain insight into the performance of an undertaker and use to check compliance with the elements described below.

Table 8. The number of supervising engineer statements reviewed

Year 2021 - 2022 2022 - 2023 Total
Number of statements received 195 225 420


99.5% compliance

The periodic inspection of a high-risk reservoir must be carried out by an inspecting engineer who is independent of the undertaker and who was not the appointed construction engineer.

At two reservoirs, the inspection did not take place in time, and we resorted to using our reserve powers to appoint inspecting engineers at these ‘orphan’ reservoirs which is described in more detail later in this report. All other reservoirs requiring an inspection were inspected.

The number of reservoir inspections and reports received is shown in the table below.

Table 9. The number of inspections and reports received during 2021-23

Inspection 2021 - 2022 2022 - 2023 Total
Number of inspections recorded this period 29 29 58
The number of inspections not carried out in time 1 1 2
Number of inspection reports received for inspection during previous period 12 0 12
Number of inspection reports received for inspection during current period 17 25 42
Number of inspections completed (report not received) 8 8 16


There is a slight increase in the number of inspections over the previous period. We attribute this increase to reservoirs which have recently been designated as high-risk reservoirs and undergone first inspection.

We expect reports to be provided soon after an inspection, but this may take up to six months, or more in exceptional circumstances. Following inspection, we maintain regular contact with the inspecting engineer until their report is received. When there is a longer delay, we seek confirmation that there are no matters which the undertaker needs to progress.

The reports for eight reservoirs where inspections had been carried out, but no reports received, have been subsequently received by us and will be reflected in our next report.

Inspecting engineers’ performance in providing reports

Inspecting engineers must provide written reasons if their report of the inspection takes longer than six months. We recorded 14 high-risk reservoirs where six months was exceeded. The greatest amount of time being 15 months at the close of the reporting period on 31 March 2023. Notable reasons provided for delays include:

  • conflict of time whilst seeking to satisfy a timebound requirement to certify statutory flood plans in England
  • dealing with uncertainties such as road widening schemes which may impact the reservoir
  • an increase in workload

We record the reasons provided for such delays and provide this as feedback to the Institution of Civil Engineers Reservoirs Committee for consideration when the engineers submit a re-application for appointment to the respective engineering panels.

Measures to be taken in the interests of safety

94.0% compliance

During an inspection, the inspecting engineer may make a recommendation as to measures to be taken in the interests of safety; these are commonly termed MIOS. These recommendations are statutory requirements, and the inspecting engineer prescribes a timescale within which the MIOS must be completed.

We do not disclose the exact nature of safety works to help protect the security of reservoirs, but we report that there were 414 MIOS current during the period, spread across 73 reservoirs. This is a 29% increase on the 320 MIOS current during the last period. Whilst the number of MIOS has increased, the nature of MIOS has not substantially changed as shown in Table 10 below.

Table 10. The proportion of MIOS by the type of work required

Type 2019 - 2021 2021 - 2023 Variance
Physical works 168 (53%) 224 (54%) +1%
Investigations 88 (28%) 106 (25%) -3%
Design review 40 (13%) 46 (11%) -3%
Emergency planning 13 (4%) 23 (6%) +2%
Monitoring 10 (3%) 17 (4%) +1%
Records 1 (<1%) 2 (<1%) negligible
Total 320 414 n/a


211 MIOS were certified as complete, with 51 (24%) of these certified later than the statutory target date provided by the inspecting engineer. This is an improvement on what we reported for the last period 2019-2021, where nearly half were completed late. At the end of the report period, 203 MIOS were outstanding, with 58 (29%) of these overdue their target date. We recorded 24 reservoirs where MIOS were not completed before the statutory target date.

Table 11 below shows those reservoirs where MIOS were overdue but later certified complete.

Table 11. Reservoirs where MIOS were overdue but later certified during 2021-23

Reservoir  Undertakers Resolution Response
Caerphilly Castle Moat Cadw 23/01/2023 Advice and Guidance
Carno Upper Dŵr Cymru Cyfyngedig 12/07/2022 No Further Action
Llyn Cae Conroy Upper Unknown ownership 27/10/2022 Other - orphan dam
Llyn Maen Bras Rhiwlas Hydroelectric Ltd. 01/06/2021 No Further Action
Llyn Peris First Hydro Company 25/10/2021 Advice and Guidance
New Pool Natural Resources Wales 06/04/2021 Advice and Guidance


We recorded 18 reservoirs as having MIOS still overdue on 31 March 2023. These are listed in Table 12 below. Four (22%) of these reservoirs are in private ownership with a variety of uses such as development potential, hydroelectric power generation and amenity. The remaining 14 (78%) are either managed directly by public authorities or by organisations which receive other public funding.

We have served enforcement notices at three reservoirs requiring the work to be done.

Table 12. Reservoirs where MIOS were overdue and uncertified on 31 March 2023

Reservoir Undertakers  Additional Comments
Canada Lake Canada Lodge Management Limited Under investigation
Carew Mill Pond Pembrokeshire Coast National Park Authority Certified Jun 2023
Coed Darcy North Site St Modwen Properties PLC Reservoir undergoing discontinuance
Cowbridge & Llanblethian FSA** Natural Resources Wales (FRM) See Management of NRW reservoirs
Crafnant Loop FSA Natural Resources Wales (FRM) See Management of NRW reservoirs
Craig Goch Dŵr Cymru Cyfyngedig Substantial increase in scope since inspection
Cwm Clydach Ownerless dam, Neath Port Talbot CBC, Water Projects Swansea Limited Orphan dam. NRW project in place
Cyfarthfa Park Lake Merthyr Tydfil CBC Under investigation
Felindre Dŵr Cymru Cyfyngedig Completion expected by September 2023
Gwastad Mawr FSA Newport City Council Notice served under s10(7)(b)
Llyn Canol National Botanic Garden of Wales Certified May 2023
Llyn Crafnant The Crafnant Trust Under investigation
Llyn Uchaf & Pwll yr Ardd National Botanic Garden of Wales Certified May 2023
Rhug Hall Lake Private landowner Under investigation
Rhyl Golf Course FSA Denbighshire County Council Under supervision of a construction engineer
Roath Park Lake Cardiff City Council Under investigation
Upper Trebeddrod Carmarthenshire County Council Awaiting certification
Waun-y-Pound Upper Fragile Limited / Hebe Lakes Limited Notice served under s10(7)(b)

** FSA – flood storage area


99.7% compliance

Where an inspecting engineer makes a statutory recommendation for maintenance of the reservoir, the undertaker is obliged to complete this. By its nature, maintenance is an ongoing activity and there is no requirement for certificates to be issued, but supervising engineers must provide a statement every 12 months on progress and highlight any maintenance not properly carried out.

We recorded a failure to complete maintenance at two reservoirs during the period. The required work has since been completed.

Monitoring and record keeping

93.7% compliance

Regular visits and equipment to monitor water levels and changes in a reservoir are important. Good record keeping of this provides a long-term view of a reservoir’s behaviour. The supervising engineers’ statements draw to our attention any breaches of monitoring and record keeping requirements. We received 29 such notifications of breaches at 25 reservoirs. During the last reporting period we reported 44 breaches at 15 reservoirs. The number of reservoirs reported has increased but there is a reduction in the number of times a breach is recorded for each one.

The level of compliance doesn’t appear to follow a pattern. We aim to produce new guidance to reinforce the importance of monitoring and record keeping, and on how supervising engineers should record and report breaches of this requirement.

Visual inspection by the undertakers

We were notified of six statutory directions as to visual inspection by the supervising engineer. This is three fewer than during the last period. No breaches of these directions have been reported.

It appears that supervising engineers are using the power to direct visual inspections judiciously, often securing the need for additional visual inspection using persuasion and influence as would be considered appropriate under the regulatory principles applicable to us as the enforcement authority.

There is variability between supervising engineers in how maintenance, monitoring and record keeping is assessed and whether it is satisfactory or not. Different engineers employ different tactics to encourage a return to compliance. The point at which different engineers choose to formally report these breaches to us also varies. We propose to produce new guidance to set out common principles to help engineers and undertakers.

Orphan reservoirs

Where there is no undertaker or owner, or we cannot identify an owner, we refer to a reservoir as being an orphan reservoir. There are currently two reservoirs in Wales which we consider to be orphans and at each we have stepped in as a matter of last resort to protect public safety. We have taken the following steps using our reserve powers:

  • appointed a supervising engineer
  • appointed an inspecting engineer to provide a report and make recommendations
  • committed to the completion of matters to be taken in the interests of safety

The safety measures are substantial and are planned across several years. The expenditure is shown in Table 13 below:

Table 13. Expenditure at orphan reservoirs over the last four years.

Reservoir 2019 - 2020 2020 - 2021 2021 - 2022 2022 - 2023
Cwm Clydach £214,000 £210,000 £77,959 £20,739
Llyn Cae Conroy Upper £- £45,000 £16,000 £18,000


Future inspections may reveal additional work is needed and we will explore opportunities to lower the level of risk by reducing the volume or decommissioning to reduce the substantial burden of ongoing monitoring and supervision by us.

Cwm Clydach

A new inspection was carried out in June 2021 from which the inspecting engineer recommends 10 safety measures. We have started work to complete these. There are difficulties and additional expense in meeting the engineering standard required when working on a Scheduled Ancient Monument and listed building. The work requires us to obtain consent from Cadw prior to starting.

There are also maintenance recommendations included within the inspection report which we cannot perform due to limitations within our reserve powers.

Llyn Cae Conroy

An inspection carried out in 2019 provided a recommendation for safety measures which we completed using our reserve powers. Many of these measures consisted of investigations to inform the next stage of work. In 2022, we arranged a further inspection and the report from that contains a single safety measure to improve protection from extreme floods.

Emergency flood planning

We expect all undertakers to prepare and maintain a flood plan which is proportionate to the inherent risk held at their reservoir. This is not required by law, and we pursue emergency planning through voluntary means. Our principal focus is to secure flood plans for all high-risk reservoirs. On 31 March 2023 we recorded the following success in securing flood plans:

Table 14. The number of reservoirs with a flood plan on 31 March 2023

Type of reservoir Number of reservoirs Number with a flood plan
High-risk reservoirs 266 187 (70%)
Other reservoirs 132 14 (11%)


We provide ongoing advice and guidance to secure flood plans for the remaining 30% of high-risk reservoirs without one. We expect to review this again before 31 March 2024, to establish whether additional interventions are necessary and how the cost of this may be recovered for an activity not required by law.


Part 2 - Management of NRW reservoirs

NRW has a dual role, being the enforcement authority and a reservoir undertaker. This poses a potential conflict of interest which we manage by separating our operational and enforcement duties at directorate level. We are required to report on the steps we have taken to observe and comply with the requirements as an undertaker.

Our Operations directorate has 37 reservoirs registered under the Reservoirs Act 1975. The purpose and designation of these is summarised in Table 15.

Table 15. The purpose and risk designation of our reservoirs

Purpose High-risk Undesignated Total
Flood Risk Management 11 2 13
Conservation 3 5 8
Welsh Government Woodland Estate 12 4 16


Our reservoirs are inspected and supervised by qualified civil engineers, and we maintain a programme of works to address any recommendations they may make.

Table 16 below shows the number of reservoirs in our care, or where we share this responsibility with a neighbour, where non-compliance has been recorded.

Table 16. The number of reservoirs non-compliant with the Reservoirs Act 1975 and the corresponding percentage of compliance for each indicator of reservoir safety.

Reservoir activity 2019 to 2021 2021 to 2023

Total number of reservoirs

35 37
Construction 0 (100%) 0 (100%)
Supervision 0 (100%) 0 (100%)
Inspection 0 (100%) 0 (100%)
Safety measures 10 (71.4%) 3 (91.9%)
Maintenance (statutory) 2 (94.3%) 1 (97.3%)
Monitoring and record keeping 4 (88.6%) 2 (94.6%)


Non-compliance recorded in our last report

In our last report, we reported non-compliance at the two following reservoirs which remained incomplete at the beginning of this reporting period. The work at these sites was completed and returned to compliance during spring 2021.

New pool (resolved April 2021)

In our last report, we confirmed a breach of section 10(6) caused by late completion of safety measures. The work was completed and certified in April 2021.

Pont-y-Cerbyd (resolved June 2021)

In our last report, we confirmed a breach of section 10(5A) caused by late completion of statutory maintenance. The work relied on the satisfactory growth of new grass which did not establish effectively over the winter period. Our supervising engineer confirmed satisfaction in June 2021.

Non-compliance recorded this period

During the reporting period we recorded new non-compliance at four reservoirs. Whilst we do not disclose the exact nature of safety works, a summary of the causes and mitigations are described for each case below.

Cowbridge & Llanblethian Flood Storage Area

We are currently in breach of section 10(6) caused by us failing to implement a measure to be taken in the interests of safety. The nature of the work is an improvement to a manual system using improved communication and automation at the site. We are having trouble securing the necessary wayleaves across neighbouring land to achieve this. Additional negotiations with BT Openreach and National Grid are underway for alternative solutions. We continue to manage the site manually and have sought advice from the inspecting engineer who has advised that the situation is “satisfactory and safe.” We are not yet certain when the measure can be completed.

Crafnant Loop Flood Storage Area

We are currently in breach of section 10(6) caused by us failing to implement a measure to be taken in the interests of safety. We did not deliver the third of four safety measures by its March 2023 deadline. Whilst planning and design progress were completed, the programme was delayed by an inability to continue works during the autumn and winter months. The works presented a hazard to fish spawning, and we had to consider the operational continuity of the structure as a flood risk management asset. The inspecting engineer has been kept informed throughout and has not considered it necessary to escalate any further urgency.

Llyn-y-Parc (resolved February 2023)

A breach of section 11(1) was caused by our failure to keep the records and to install the instruments required to obtain the records. Additional maintenance was carried out and the breach resolved in February 2023.

Dyffryn Conwy Flood Storage Reservoir (resolved February 2023)

Two instances of a breach of section 11(2) occurred resulting in inadequate records being kept. Although the prescribed routine surveillance visits are carried out, we failed to record water levels daily during high level impoundments as recommended by the inspecting engineer which meant our monitoring records were incomplete at times when human resources were required elsewhere during flood events.

We have continued to provide training for our ‘reservoir keepers’ to fulfil our maintenance, monitoring and record keeping duties. Our ability to visit and check all reservoirs was tested during times of flood, and we are looking to make improvements in this area.


Reservoir improvements

We have progressed a programme of reservoir improvements at our reservoirs, aligned to their purpose for either flood risk management or as part of our land, conservation, and woodland management.

We have completed 37 MIOS across 12 of our reservoirs in this reporting period, with a further 25 to complete over the next few years.

In March 2023 we held an official opening of our major works at Llyn Tegid which plays a vital role in regulating the river Dee, storing river water, and allowing controlled release to manage flood risk and enable abstraction for water supply. This work protects 800 properties from extreme weather and has balanced flood risk and water resources with the demands of a highly scenic and popular tourist destination lying next to Bala within the Eryri national park. The work included placing 13,000 tonnes of locally sourced granite whilst also maintaining and improving two sites of special scientific interest, a special area of conservation and a Ramsar wetland of international importance.

We are proud of our work at Llyn Tegid. Our completion of this major engineering and landscaping project was driven not only by reservoir safety but also by our wellbeing goals. Through extensive public consultation and participation, we ultimately delivered multiple environmental and social benefits. The project included the planting of over 300 trees, improved footpaths for all abilities, new seating areas and the creation of five hectares of restored natural habitats and new areas of wildflower meadows.

The Llyn Tegid project is shortlisted in the ICE (Institution of Civil Engineers) Wales Cymru Civil Engineering Awards with the award ceremony to be held on 22 September 2023.

We delivered improvements to Pen-y-Gwaith, a historic reservoir within the Welsh Government Woodland Estate. The works comprised of significant embankment raising and the installation of an enlarged spillway, ensuring the reservoir’s safe operation. Pen-y-Gwaith has many important characteristics that the project had to address in addition to the requirements set under the MIOS works. These include the protection of the Site of Special Scientific Interest, maintenance of historical mining structures, abstraction for a private water supply, recreation and our aspirations under the Well-being of Future Generations (Wales) Act 2015 to provide safe access to the countryside.

Our reservoir improvement schemes look at long-term improvements that can provide environmental, economic, and social benefits to the many people that interact with our assets. Pen y Gwaith reservoir was also reviewed to identify where the project could make biodiversity improvements, and did so, by planting 145 native deciduous trees, including birch and ash. We also have a responsibility to consider how our construction emits carbon dioxide into the atmosphere, to reduce our emissions we were able to use local stone from our own nearby quarry hugely reducing our carbon footprint and overall costs.

We consider it likely, given the age of many of our reservoirs, that inspecting engineers will recommend further recommendations in the interests of safety over the next two-year period. The extent of these works is unknown, but the safety of our reservoirs remains a priority area of work.

Flood plans and exercises

We have committed to provide flood plans for all our reservoirs before the end of 2023 including those that are undesignated (not high-risk).

The creation of our flood plans includes an annual review to ensure they remain current and our commitment to testing. We plan to carry out at least one exercise every year. The lessons we learn from these exercises are shared with emergency responders and other professional partners as appropriate.


Incidents at NRW managed reservoirs

We recorded seven reportable incidents; these have ranged from deformation cracking during the drought last summer to suspected leakage on a spillway. Of these reportable incidents two have resulted in capital projects to repair the reservoirs.

Staff training and development

We have continued to train reservoir keepers to undertake weekly duties for monitoring and maintenance. After initial training, each keeper receives an annual refresher course to keep their knowledge and confidence current.

We employ two reservoir asset inspectors that predominately cover North and Mid Wales where most of our reservoirs are located. We also have a dedicated hydrometry and telemetry specialist who has enabled upgrades to our telemetry equipment. This has improved our operations to record and provide evidence of water levels and flows.

The significant demand for construction projects which followed the registration and first inspection of reservoirs (described in our previous reports), has led us to hold a ‘lessons learnt’ workshop every six months to ensure reservoir project managers, engineers, contractors, and operational managers can share experience and best practice which we incorporate into future projects. 


Part 3 - Forward look

Wales has a good reservoir safety record, but we recognise the importance of continuing to strive for higher standards, and how crucial it is to ensure our flood risk infrastructure is fit for the long-term.

In May 2021, we received Professor David Balmforth’s report into how reservoir safety is regulated (Reservoir review: part B (2020) - GOV.UK ( Whilst written primarily for England, we recognise that many elements of the report are not constrained by boundaries, and we consider his findings to be relevant for Wales. There are 15 recommendations and 52 sub-recommendations. Not all apply to us; some are for reservoir owners, engineers, the Government, and the Institution of Civil Engineers.

To implement many of the recommendations, the law will need to change, and the development of proposals will take time. The Reservoirs Act 1975 applies to England and Wales, and with Welsh Government, we are working with Defra and the Environment Agency to understand the changes which may be needed and to devise a realistic timetable for this. It is too soon to comment on how the current law may need to change. We think there are clear benefits in maintaining cross-border harmony where practicable, but we accept there may be some divergence.

We have committed to working with Defra and the Environment Agency in a project to better define hazard thresholds. The next two years should realise the results from this work and help us improve our regulation and inform potential future legislation.

Additional work in collaboration with the Environment Agency will improve our guidance and processes for the submission of post-incident reports to help share the learning from incidents and near misses.

Our approach to implementing these recommendations will incorporate Wales’s principles of the sustainable management of natural resources (SMNR). We will:

  • Be adaptive in our management
  • Consider the appropriate spatial scale for action
  • Collaborate and engage with others
  • Use public participation to ensure we understand all the issues
  • Gather and use evidence to make our decisions
  • Seek multiple benefits
  • Take account of short-, medium- and long-term consequences
  • Take preventative action
  • Build resilience

Our corporate plan to 2030 sets our vision and direction for nature and people thriving together. This plan helps focus our work at reservoirs to:

  • work with other undertakers in Wales to share knowledge and lessons learnt
  • protect communities from flooding, and provide resilience to the impacts of climate change
  • update reservoir procedures to enable our staff to have confidence and familiarity in managing our assets
  • ensure we continue to undertake maintenance and construction on our dams whilst considering the needs of our visitors
  • reduce our carbon emissions
  • use local contractors and suppliers to help safeguard a pool of reservoir knowledge and experience in Wales
  • review the value and opportunities our reservoirs hold, and where appropriate re-purpose them, for example for fighting forest fires, preventing habitat loss and promoting habitat recovery, or used to enable people’s fitness and enjoyment of the Welsh countryside

The safety of Wales’s reservoirs is clearly important, and the purpose of our regulation is to provide reassurance to the public that reservoir undertakers are doing all that should be expected of them to keep their reservoirs safe.

Undertakers generally take responsibility for their reservoirs and compliance remains high, but this report has drawn attention to those areas where improvements are needed, for example better routine maintenance and monitoring and swifter implementation of safety measures. Addressing these shortfalls is our priority during the next two years.

Wales is unique in being the only UK nation to reduce the reservoir capacity threshold to 10,000m3. The effects of bringing these smaller reservoirs into regulation are now being felt. Securing the appointment of engineers has been challenging with undertakers who are less familiar with what is required and often surprised by the financial cost. The first-time inspection of aging reservoirs has revealed many to be in poor condition with safety measures to be implemented, whilst the undertakers must also devise an appropriate operational safety regime, often for the first time.

We are continuing to review our approach to regulating reservoir safety and we will continue to work with stakeholders and other UK partners to make improvements where needed.

From 1 April 2024 we intend to produce our report annually. This increased frequency is a response to the growing number of requests for information from the reservoir safety sector and to keep all stakeholders informed during a period where there is a potential for change.


The effects of the 2016 Regulations are now clearer. The rate of registration of smaller reservoirs with a capacity between 10,000 and 25,000 cubic metres has slowed. The total number of registered reservoirs, at 397, represents almost a doubling in the number of regulated reservoirs. We expect to receive further registrations but consider the numbers to be low and for reservoirs smaller in their dimensions.

We have undertaken dam break flood mapping and used our power to designate high-risk reservoirs where we think an uncontrolled release of water could endanger life. Our flood mapping has given us a better knowledge of the flood hazard held by smaller reservoirs. Many do not need designation as high-risk reservoirs because they do not pose a risk to life. These remain on the public register but without the need for inspection and supervision by engineers. We monitor these for changes over time and signpost our guidance.

We have advised and prompted the first-time appointment of construction, inspecting and supervising engineers for high-risk reservoirs, and the need for undertakers to implement engineers’ recommendations. We see that over half of the smaller reservoirs brought in regulation could pose some hazard to life and need maintenance. The undertakers now face the reality of financing the appointment of engineers, training staff, and employing contractors.

The data from Part 1 of this report show we must improve our regulatory approach further to attain improved compliance are developing new guidance to help this.

We continue to work with Welsh Government and with UK counterparts to explore options for improving the regulatory framework.

Like the early 20 Century incidents which prompted the first legislation, the incidents at Ulley reservoir in 2007 and at Toddbrook reservoir in 2019 have both caused Government to review how reservoir safety is delivered in the UK. We are responding to the findings from these incidents by improving our regulation under the current law and working with the sector and with Government to produce further improvements. This review process suggests a time of change and to provide more frequent analysis of our work, we intend to produce our report on an annual basis starting from April 2024.

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