The Susquehanna River flows 464 miles from Cooperstown, New York to Havre De Grace, Maryland. It drains an area of more than 27,000 square miles (including roughly half of the state of Pennsylvania) and is the single largest source of fresh water flowing into Chesapeake Bay. The river provides nearly half of the Bay’s freshwater, 41% of its nitrogen, 25% of its phosphorus and 27% of its sediment load.
Conowingo Dam is located on the Lower Susquehanna River about 10 miles upstream from where it flows into the Chesapeake Bay at Havre De Grace, Maryland. Like all hydropower dams, Conowingo has replaced a free-flowing section of the Susquehanna River with a 14 mile long, 9,000 acre reservoir, fundamentally altering the river’s ecology. Conowingo – along with the four other hydropower facilities on the river – has changed seasonal river flow, blocked the migration of shad, herring, eel, and other fish, destroyed fragile aquatic habitat, devastated the mussel communities that naturally filtered the Susquehanna’s water, killed millions of fish caught in hydroelectric turbines, and altered the river’s natural ability to transport nutrients and sediment.
Conowingo also traps polluted sediment from the Susquehanna River in its reservoir. There are nearly 200 million tons of sediment, nutrients, and other pollutants from the Susquehanna River trapped behind the dam. During floods caused by large storms like Hurricane Agnes and Tropical Storm Lee, some of the sediment trapped behind the dam is scooped up along with the other sediment flowing down the Susquehanna River and sent downstream to the Bay. This sediment trapped behind Conowingo has an impact on upper Chesapeake Bay water quality.