The Severn River is a tidal estuary 14 miles long, located in Anne Arundel County in the U.S. state of Maryland, south of the Magothy River and north of the South River. The Severn has a watershed area of 81 square miles, or 69 square miles of land. Thus, its total watershed area is 15% water. Its source is the beginning of the non-tidal nine-mile long Severn Run in …The Severn River is a tidal estuary 14 miles long, located in Anne Arundel County in the U.S. state of Maryland, south of the Magothy River and north of the South River. The Severn has a watershed area of 81 square miles, or 69 square miles of land. Thus, its total watershed area is 15% water. Its source is the beginning of the non-tidal nine-mile long Severn Run in northwestern Anne Arundel County in Severn, Maryland. The river enters the Chesapeake Bay near the major port city of Annapolis, also the capital of Maryland. Most famous for the United States Naval Academy campus situated at the mouth of the river, the Severn provides an access point to the Chesapeake Bay not just for midshipmen but also for fishermen and pleasure boaters. Several tributary creeks drain highly developed areas, including Weems Creek and its nontidal portion Cowhide Branch, which drain most of the Annapolis Mall and the Anne Arundel Medical Center.