Aerial survey data (1968-1989) and water gauge readings (1958-1989) were examined to detennine trends in and relationships between canvasback (Aythya valisineria) populations and water levels at Catahoula Lake, Louisiana. Wintering canvasback populations at Catahoula Lake have increased over the past 21 years. A peak population estimate of 78,000 canvasbacks was recorded in January 1988. There was a significant relationship between increases in wintering canvasback numbers and increased November water levels. No significant changes in December or January water levels nor relationships between wintering canvasback numbers and December or January water levels could be detected. In recent years, Catahou1a Lake has become one of the most important canvasback wintering areas in North America. We conclude that the increased availability of open water feeding habitat has been a major factor in the increased usage of Catahoula Lake by canvasbacks.