The reservoirs are a 391.3-hectare (967-acre) biological Site of Special Scientific Interest, of which 316.3 hectares are in London and 75 hectares in Essex. They are comparatively shallow and provide open water habitat for wildfowl, gulls and waders.[1]
Since the 1950s, the reservoirs have been providing a refuge for wildfowl while they are vulnerable during the late summer moult, and in some years, moulting flocks of great crested grebe have also used the reservoirs as a refuge. The reservoirs have also been used by migratory birds as a stopover site in autumn and spring, and yellow wagtail regularly breed here. A total of over 85 species of wetlands birds have been recorded at the site.[1]