These are a further enhancement of retention ponds that incorporates shallow areas planted with marsh or wetland vegetation.  They provide a much greater degree of filtering and removal of nutrients by algae and, to a lesser extent, by plants.  Inlet and outlet sumps will improve performance and are recommended, since excessive sediment can quickly overwhelm the shallow area.

Only specially constructed wetlands should be used to treat surface water.  It is not normally an acceptable practice to lead surface water into an existing natural wetland area.

Constructed wetlands have proven to be effective in many developed countries, providing moderate to high levels of pollutant removal throughout the year.  Constructed wetlands, designed by specialist consultants, will enhance their performance and longevity. A review of constructed wetlands was published by CIRIA in 1997

SUDS such as ponds and wetlands provide additional green areas and interesting water features within developed areas.  They are useful for urban recreation and pollution tolerant wildlife.  They can also provide corridors for wildlife to move between suitable habitats in urban areas

View sites in Wales with a Wetland system.