What to think about when planning your constructed wetland


Understand what you expect the constructed wetland to achieve and any additional benefits.

Constructed wetlands are recognised as a treatment option for contaminants and nutrients, including the removal of phosphorus.

Constructed wetlands shouldn’t be used as a substitute for reducing pollution at source.

You will need to be able to show that you have considered ways of avoiding or reducing the problem before using a constructed wetland


Constructed wetlands should be sited in an appropriate place for what they are being constructed to do.

Constructed wetlands must not be sited on existing priority habitats listed under Section 7 of the Environment Act, including existing natural wetland habitat.

If the proposal is likely to affect a Special Area of Conservation (SAC), a Habitats Regulations Assessment (HRA) will be required.

Read more about Habitat Regulations Assessments on the Welsh Government site

If the proposal is within a Site of Special Scientific Interest (SSSI) consent will be required. Proposals within protected sites will not be allowed unless they do no harm or are beneficial to the site.

Constructed wetlands must not increase flood or coastal inundation risk or pollute groundwater, especially Source Protection Zones for water supplies.


Your design should ensure that all the following are covered:

  • ability to achieve the water treatment and / or water storage needs
  • slowing and storing water to achieve the required hydraulic retention times
  • sizing
  • seasonal impacts
  • risk of leakage to ground from within the wetland, or during the construction of it, this is to be avoided
  • maintenance needs
  • habitat creation
  • requirements of other legislation or permissions.

Appropriate design standards should be met and use of an accredited consultant is recommended.

Advice can be obtained from CWA (Constructed Wetland Association).


Clarify responsibilities and liabilities with all involved parties, including the land-owner.


Consider the cost of installing, monitoring and maintaining your constructed wetland for its anticipated lifetime.


Think about what waste will be created through the construction, maintenance and decommissioning phases and how it will be managed.


It is recommended that constructed wetland designs are precautionary when calculating the rate of nutrient and contaminant removal when sizing the wetland.

Ongoing monitoring should identify any poor performance early so an adaptive management plan can be implemented.

Monitoring and maintenance

You should be able to demonstrate the ability to manage, monitor and maintain the system for its lifetime.

Other regulatory requirements

You may need planning permission from your local planning authority.

Find your local planning authority on the Welsh Government website.

You may need building regulations permission.

Read about Building Regulations on the Welsh Government website.

You may need approval for your drainage system.

Download advice about sustainable drainage systems (SuDS) from the Welsh Government

You may need a Flood Risk Activity Permit

Apply for a Flood Risk Activity Permit

You may need a water resources licence for abstraction or impoundment.

Apply for a water abstraction or impoundment licence

If the proposed site of your constructed wetland is in a protected area, your planning authority may need to carry out a Habitats Regulations Assessment.

Read about HRA on the Welsh Government website

You may need to demonstrate that the constructed wetland will not cause deterioration to a water body.

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