Diving ducks wintering in Chesapeake Bay during the last 50 years have accounted for 23% of Atlantic Flyway and 9% of North American populations based on aerial surveys. Continental and local factors have affected these population changes. Loss of submerged aquatic vegetation (SAV) due to degradation of water quality, has been a contributing factor, although, many other factors related to human population increases have been implicated in the changes in the distribution and abundance of diving ducks.
Factors affecting diving duck populations include direct and indirect causes, including excessive development of Bay tributaries, increased year-round boat traffic, and increased levels of contamination. Food habits indicate major changes in some species of diving ducks especially the pochards, since SAV has declined. Other species of diving ducks, show little changes in food habits and still are feeding on mollusks species that have traditionally formed the bulk of their diets. Species, like the pochards, that feed in shallow water are probably more affected by environmental changes in the Bay than species that feed in deeper water.