Historically a trade routein southern Maryland, St. Mary’s River is one of the many rivers that feed into the Potomac River.

Geography
St. Mary’s River stretches over 22 miles southeast past St. Mary’s City to meet with the Potomac River. The river is located entirely in St. Mary’s County, Maryland, with its principle source at St. Mary’s Lake. The lake is artificial, created by a flood control damn in the river’s watershed. A watershed is the area of smaller bodies of water, such as creeks, streams, and marshes that feed into a larger body of water.

The watershed for St. Mary’s River takes up approximately 44,800 acres (70 square miles). The river flows through gentle hills and valleys in the northern portion and through a variety of landscapes, including woodland and swamp. The land becomes nearly flat in the lower tidal portion where St. Mary’s River nears the Potomac.

History
Historically, the river was used by American Indians as far back as 3000 BCE. for fishing and transportation. European settlers used what was called St. George’s River for the same reasons. Establishing St. Mary’s City, the fourth permanent settlement in British North America”, the settlers took up residence in an area that the Yaocomaco Indians were in the process of abandoning. The original settlers were primarily Catholics fleeing religious persecution from England, renaming the village in honor of Queen Henrietta Maria.

For a time, St. Mary’s City was Maryland’s capitol and its largest port, with Port Tobacco second. Both exported tobacco to England. The river’s port of St. Mary’s City was eventually abandoned for Annapolis, a city that was more central and convenient to the growing colony. The city also had a better harbor than St. Mary’s. Leonardtown became the county seat soon afterward. St. Mary’s City was never rebuilt after being abandoned, and has since become an archeological site and tourist attraction.

St. Mary’s River State Park
The northern end of the river was eventually turned into St. Mary’s River State Park, encompassing 250-acre St. Mary’s Lake, an artificial lake created by damming of the St. Mary’s River watershed (Site 1) and a 2,200-acre protected wildlands and managed hunting area further south on the opposite bank (Site 2). Several species of freshwater fish live in the lake and river, including largemouth bass, bluegill, chain pickerel, and sunfish. The lake is a popular spot for fishing and boating, with trails around the lake for hiking, horseback riding, and biking.

Hurry, Silas D. Once the Metropolis of Maryland: The History and Archaeology of Maryland's First Capital. St. Mary's City, Md.: Historic St. Mary's City Commission, 2001.