Here is a quote from the Wikipedia article about the Severn River in Maryland.
The Severn has a watershed area (including the water surface) of 81 square miles (210 km2), or 69 square miles (180 km2) 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.This river looks like a huge lake or part of the ocean. Technically at this point, it is an estuary because it has tidal fluctuations. We cross this river several times a week traveling to the Annapolis Stake Center of The Church of Jesus Christ of Latter-day Saints. The large building on the shore that looks like a mansion is a care center.