Waterfowl populations were monitored at Lake Wales, Florida, over a three· year period to determine factors associated with their abundance and aggregations. Monthly water level, water temperature, aquatic vegetation percent cover and percent frequency of occurrence, and chlorophyll a data were correlated and regressed. Significant models were derived to describe variation in total waterfowl, ring-necked ducks, canvasbacks and American coots. Interactions of introductions of two exotic species. grass carp (Ctenopharyngodon idella Val.) and hydrilla (Hydrilla verticillata Royle) with waterfowl populations were discussed. A decline in numbers of some waterfowl species was attributed to changes in hydrilla abundance as a result of the combined effects of grass carp, water level and other factors.