The East Sussex Biodiversity Partnership describes Bewl Water as follows.

Bewl Water reservoir is the largest expanse of open water in Southern England. Bewl Water is extremely important for large numbers of waders and wildfowl during the winter and as a stopping point during migration. The gull roost comprises tens of thousands of gulls in winter. A total of 171 recorded species includes rare visitors such as Great Northern Diver, Smew, Black-winged Stilt and Grey Phalarope, and wintering numbers of Great Crested Grebe, Little Grebe, Cormorant, Wigeon and Teal. Large numbers of Great Crested Grebe breed here and there are usually numbers of migrating waders such as Spotted Redshank, Greenshank, Wood Sandpiper and Common Sandpiper. The reservoir also provides habitat for dragonflies, with 20 species regularly recorded.