Merrymeeting Bay is a 4330-ha freshwater tidal ecosystem in mid-coast Maine that historically provided important stopover habitat for migrating waterfowl. To better understand a substantial decline in the number of ducks foraging in the ecosystem over the past fifty years, we reconstructed a history of environmental change using oral histories, aerial photography, and field experiments. Our studies revealed profound environmental change throughout the 20^th century that likely influenced the capacity of the ecosystem to support migrating waterfowl. Ironically, the unregulated discharge of industrial and municipal wastes and high rates of sedimentation associated with land use in the middle decades of the 20^th century probably enhanced the extent and productivity of intertidal, emergent plant communities including key forage plant species. However, over the past 30 years, primary wastewater treatment and regional reforestation have reduced the rates of nutrient loading and sedimentation, thereby diminishing the emergent vegetation. Reinforcing this decline in emergent vegetation, a precipitous decrease in submerged aquatic vegetation between 1956 and 1981 was likely related to extreme water turbidity. The collapse of subtidal aquatic vegetation would have reduced the variety and quantity of food items available to waterfowl. These local environmental changes coincided with regional declines in several duck species migrating along the Atlantic flyway. Therefore, both regional processes affecting the overall duck populations as well as local environmental change likely influenced the abundance of waterfowl using this site over the past 50 years.