Southern Maryland is surrounded by water. The Chesapeake Bay, the Patuxent River, the Potomac River, and the St. Mary's River all bound the tri-county area. The Chesapeake Bay is still a major navigable route for freight ships to and from the port of Baltimore. Likewise, ships still navigate the Potomac to and from Washington, D.C. For this reason, the area is rich in lighthouse history, both active and inactive.