The Patuxent River is a tributary of the Chesapeake Bay in the state of Maryland. There are three main river drainages for central Maryland: the Potomac River to the west passing through Washington D.C., the Patapsco River to the northeast passing through Baltimore, and the Patuxent River between the two. The 957 square miles (2,479 km²) Patuxent watershed had a rapidly growing population of 590,769 in 2000. It is the longest river to be located entirely within the state of Maryland.

History
The Middle and Little Patuxent watersheds include nearly all of Columbia, Maryland, including its downtown urban Lake Kittamaqundi and Wilde Lake. Columbia is a large planned community in Howard County that opened in 1967. Columbia's major downtown roadway is called Little Patuxent Parkway, and Maryland Route 175 in East Columbia was known as the Patuxent Parkway until May 2006, when it was renamed for Columbia's founder, the late James Rouse, and his wife, Patty. It was the largely unchecked erosion from this late 1960s and 1970s building spree that contributed the bulk of the Patuxent River's highest and most damaging sediment, siltation, and pollution levels to date downstream. This in turn led to a nearly complete destruction of a once thriving seafood industry along brackish portion of the river.
The river's best-known environmentalist, Bernie Fowler, as an early-1970s Calvert County Commissioner, led the way in a lawsuit filed by downriver Charles, Calvert and St. Mary's counties against upriver counties. The lawsuit forced the state, the upriver counties, and the U.S. Environmental Protection Agency to enact pollution control measures. The 1985 total of 200,000 tons of sediment reaching the Chesapeake annually was reduced to 130,000 by 2004. The Patuxent is a rarity among Chesapeake watersheds in that most of its harmful phosphorus and nitrogen nutrient overloads come from its ever-increasing areas of urban runoff, and less from its other two largest contributors, point sources (industrial, sewage, etc.) and the declining agricultural areas.
Fred Tutman is the Riverkeeper for the Patuxent. There is only one official Riverkeeper whose role is to protect and improve the quality of the river's water.
Over the past 50 years, nationally-recognized land preservation efforts in this part of Maryland have saved tens of thousands of acres from the Baltimore-Washington bedroom community sprawl. The southern half of the U.S. Army's Fort Meade was added to the Patuxent Wildlife Research Center, which, at 12,300 acres (50 km²), is the second largest contiguous public park-refuge within 30 miles (50 km) of either Washington or Baltimore. It is located midway between these two cities. The contiguous public area of 8,575 acres (35 km²) centered on Jug Bay, 42 miles (68 km) upriver from the Chesapeake, form the fifth largest such Baltimore-DC preserve and largest tidewater one and consist of the Jug Bay Wetlands Sanctuary, the Merkle Wildlife Sanctuary, and the Jug Bay component of the Patuxent River Park. The 6,600 acre (27 km²) Patuxent River State Park in the uppermost part of the basin is the seventh largest.