Sixty percent of the total fresh water flow to the Chesapeake Bay originates from the Susquehanna River - more than any other river in the Bay watershed. Based on data from the US Geological Survey, this river, which is below the Conowingo Dam, discharges about 18 billion gallons of fresh water each day - a volume equivalent to filling Baltimore’s M&T Bank Stadium more than 70 times daily. This amount of fresh water flowing into the Bay can vary widely. Over the past 40 years, the daily average flow from the Susquehanna to the Bay has varied from 0.3 to more than 720 billion gallons per day.

The Bay’s other major fresh water river sources are the Potomac River (about 20 percent), the James River (about 12 percent), and about 6 percent comes from a combination of rivers draining smaller watersheds – the York, Rappahannock, Patuxent and Choptank. Other significant sources of fresh water to the Bay include direct rain and snowfall and an unknown amount of groundwater flow.

Fresh water flow to the Bay depends on many factors. Rain or snowmelt runoff that may briefly flood streams and rivers increases fresh water flows to the Bay. Long periods of drought will lower shallow ground water levels that provide streamflow when there’s no runoff. The water we withdraw for drinking, irrigation or industrial use, add as wastewater, or store in and release from reservoirs can also affect daily flows to the Bay.

- Sherm Garrison
Chief, Water Quality Program
Tidewater Ecosystem Assessment Division
Maryland Department of Natural Resources