Susquehanna National Wildlife Refuge and surrounding areas were once covered with wild celery, pond weeds, redhead grass and other desirable waterfowl food sources. At their peak, waterfowl included over 500,000 canvasback and redhead ducks as well as over 200,000 American wigeon. These rich areas of aquatic growth began declining in the 1960's due to changes in the water quality and quantity. Development above the Conowingo Dam caused more rapid drainage and greater water flow through the dam. Currents in the upper Chesapeake Bay deposited heavy loads of silt in the Susquehanna flats area. The remaining waterfowl vegetation was destroyed by Hurricane Agnes in 1972. Only a few thousand geese remained around the refuge during winter.