The Susquehanna, Potomac, Rappahannock, York and James rivers are the five major rivers that flow to the Chesapeake Bay.

Altogether, more than 100,000 streams, creeks and rivers thread through the Chesapeake Bay watershed.

Fresh water enters the Chesapeake Bay primarily from its rivers and streams. Fresh water also enters via rain, snow and groundwater.

The Chesapeake Bay’s salinity gradually decreases as you move north and increases as you move south. Salinity also varies widely from season to season and from year to year, depending on the amount of fresh water flowing from the Bay’s rivers.

An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. Some river mouths are estuaries. For example, the tidal portion of the Hudson River in New York is an estuary.

Fish passageways allow shad and other anadromous fish to pass over dams and reach their upstream spawning grounds. There are five major fish passageway designs used in the Chesapeake Bay watershed: denil, steeppass, vertical slot, pool and weir, and fish lifts.

Fish passage is the ability of fish to migrate up rivers, streams and other waterways, often to access spawning or rearing areas. Barriers to fish passage (which can include road culverts, dams, dikes and other obstructions) can reduce the distribution and habitat available to anadromous fish and, in some cases, eliminate fish populations altogether.

Shad are anadromous, which means they migrate from the ocean to spawn in freshwater rivers and streams.

Shad spend most of their lives in the ocean. They migrate to freshwater rivers and streams to spawn. After hatching, young shad slowly migrate downstream, eventually leaving the Chesapeake Bay for the ocean.