Wintering waterfowl community structure and their association with lake characteristics were studied in the Cotswold Water Park, a complex of more than 120 gravel pit lakes in southern England. The major distinction in community types was between assemblages dominated by diving waterfowl and those dominated by dabbling waterfowl. The trophic status of lakes was found to be a major determinant of community structure: young lakes in the early stages of a natural process of eutrophication tended to support the most diverse assemblages of diving waterfowl. The abundance of individual species was strongly related to lake size and assemblage type. Some effects of food supply and the recreational use of lakes were also apparent. The relevance of the findings for the sustainable value of the lakes for wintering waterfowl is discussed.