The ponds in Denman Park are home to a wide variety of wildlife but have been subject
to pollution from a range of sources in recent years, and have been overcome with excessive vegetation.
A project is underway to restore and improve the quality of the ponds, increase and restore
habitat and biodiversity both in and around the ponds.

Link to leaflet to explain the work being done

Here is a case study that provides further background on the need to use a downstream defender unit in conjunction with a wetland water treatment system

Two major pieces of work are due to start in Denman Park this week. As previously trailed, one contractor will be extending and improving the path network, and another will be installing a filtration system for the ponds, known technically as a “downstream defender”

The downstream defender unit contract will last around 9 weeks finishing around the end of June.  During that time the road into the park and the tennis courts car park will remain open except for temporary closures associated with the delivery of large items and the formation of a maintenance access to the downstream defender unit.  Unfortunately, the path into the park from the car park will need to be closed for the duration of the works.  The works require the excavation of a 6 metre deep hole, the storage of excavated soil and the installation of new pipework in addition to the downstream defender unit.