Over 270 species of birds have been recorded at Chew, an internationally important site for wintering and migrating wildfowl. From late July to February, up to 4,000 ducks (Anatidae) of twelve different species may be present, including internationally important numbers of northern shoveler ("Anas clypeata") and gadwall ("Anas strepera"). Up to 600 great crested grebes ("Podiceps cristatus") gather to moult on the lake in autumn. Data on bird species and their numbers on the lake, dating back to the first "ringing" in 1964, is available from the Chew Valley Ringing Station.