the area. There are also more recent alluvial deposits beside the course of the River Chew. Birds 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. Numerous other birds can be seen, especially during the spring and autumn migration. Sand martins (Riparia riparia) arrive early and can usually be seen hawking over the water for insects in the second or third week of March. Flocks of tits (Paridae), swallows (Hirundinidae) and terns (Sternidae) can regularly be seen. Waders, such as lapwings (Vanellus vanellus), dunlin (Calidris alpina) and common snipe (Gallinago gallinago), are attracted to the muddy shores if the water level drops in autumn. By midwinter up to 55,000 gulls, mostly black-headed gull (Chroicocephalus ridibundus) and common gull (Larus canus), may be roosting. Good numbers of reed warblers (Acrocephalus scirpaceus) and sedge warblers (A. schoenobaenus) nest in the fringing reeds, along with grebes (Podicipedidae) and Eurasian coots (Fulica atra). Much of the management work carried out in the nature reserve is aimed at encouraging ducks to breed, and small numbers of tufted duck (Aythya fuligula), common pochard (Aythya ferina), common shelduck (Tadorna tadorna) and gadwall raise broods most years. Recent breeding successes also include water rail (Rallus aquaticus) and Cetti's warbler (Cettia cetti). A wetland reserve has been created at Heron's Green Pool on the opposite side of the causeway to the lake. A shallow pool fringed with sedges (Cyperaceae), rushes (Juncaceae) and reedgrasses (Calamagrostis) and surrounded by lightly grazed, rough grassland may also prove attractive to snipe and lapwings. Fish In late summer large shoals of roach (Rutilus rutilus) and perch (Perca fluviatilis) fry congregate around the margins and weed beds, which are predated by the brown trout (Salmo trutta morpha fario) and rainbow trout (Oncorhynchus mykiss). Chew Valley also holds a large population of pike (Esox lucius), and fishing for these is permitted at certain times of the year. Insects Aquatic midges (Chironomidae) provide the highest