Stream flow and ground water carry nutrients, sediment, and contaminants into the Chesapeake Bay. The variability of stream flow due to seasonal and yearly changes in rainfall and ground water effects salinity, dissolved oxygen, and water clarity in the Bay. Ground-water contributes to stream flow and is also measured. The USGS measures stream flow throughout the Bay watershed and computes the amount entering the Bay each month. Visit the monthly water conditions page for a synopsis of the stream flow and ground water levels in the Bay watershed.

The USGS investigates the occurrence, quantity, quality, distribution, and movement of surface and underground waters and disseminates the data to the public, State and local governments, public and private utilities, and other Federal agencies involved with managing our water resources. Water resources data collected at approximately 1.5 million sites in all 50 States, the District of Columbia, and Puerto Rico is available online from the National Water Information System (NWIS) at http://nwis.waterdata.usgs.gov/usa/nwis/rt. Stream flow and ground-water quantity and quality data for individual States and sites in the Bay watershed is also available online from NWIS. Water use data is available on the USGS Water Use in the United States site at: http://water.usgs.gov/watuse/.