The Patapsco River flows 39 miles through central Maryland. The tidal portion of the river forms Baltimore Harbor. The area is heavily developed and urbanized, but the Patapsco River is still well-known for its diverse fish populations. The river’s low gradient and shallow bed create scattered deep pools that are attractive to fish species such as trout, bass, and sunfish. The tidal Patapsco River is crossed by the Baltimore Harbor and Fort McHenry Tunnels and the Francis Scott Key Bridge. The Back River, a small system of urban and suburban streams, empties in the Bay north of Baltimore City. This river system is similarly impact by human development and is a popular recreational area. (Based on Baltimore County Watershed Management Program and Maryland Department of Natural Resources.)