Patapsco River

The Patapsco River is a 39-mile river in central Maryland that flows into the Chesapeake Bay. It is an important waterway because its tidal part forms the harbor for the city of Baltimore.

Together with its South Branch, the Patapsco River marks the northern border of Howard County, Maryland. The name "Patapsco" comes from an Algonquian word meaning "backwater" or "tide covered with froth," showing the river's connection to the tides of the Chesapeake Bay.

History

Captain John Smith was the first European to explore the river. He noted it on his map in 1612 and called it the Bolus River. The river’s current name likely comes from the Algonquian language, meaning “at the jutting ledge of rock,” referring to a spot near the river.

The Patapsco River played an important role in Maryland’s early industry. Mills and factories lined its banks, powered by small dams. The Baltimore and Ohio Railroad’s first main line followed the river valley. Notable structures included the Thomas Viaduct, still in use today, and Bloede’s Dam, built in 1906 to produce power.

In March 2024, a container ship struck and partially collapsed the Francis Scott Key Bridge, which crossed the river. The river’s mouth forms Baltimore Harbor, where the Battle of Baltimore occurred during the War of 1812. It was here that Francis Scott Key wrote “The Star-Spangled Banner,” which later became the national anthem of the United States.

Course

The South Branch of the Patapsco River is 19.4 miles long and starts at Parr's Spring, where Howard County, Carroll County, Frederick, and Montgomery counties meet. It begins at an elevation of 780 feet on Parr's Ridge, just south of Interstate 70. The South Branch marks the southern edge of Carroll County and the northern edge of Howard County.

The North Branch flows 20.9 miles southward from Carroll County. The Liberty Dam and its reservoir on the North Branch are important for the water supply of Baltimore.

The main part of the Patapsco River starts where the North and South Branches meet, near Marriottsville, about 15 miles west of downtown Baltimore. For most of its length, the river flows through a narrow valley. Patapsco Valley State Park runs along 32 miles of the river and its branches, covering 14,000 acres. The river carves a deep gorge with rocky cliffs and waterfalls inside the park.

In its last 10 miles, the river forms a large tidal inlet of the Chesapeake Bay. The area includes two branches of the harbor: the Middle Branch, where the Gwynns Falls flows, and the Northwest Branch, where the Jones Falls flows. The inner part of this area serves as the harbor for Baltimore. The Patapsco estuary lies south of the Back River and north of the Magothy River.

Tributaries

The Patapsco River has a watershed of 950 square miles (2,460 km²). It has many smaller streams that flow into it, including Deep Run, Board Run, Roaring Run, Liberty Reservoir, Piney Run, and many others. These streams come from different areas such as Carroll County, Baltimore County, and Howard County.

Ecology and conservation

When Bloede's Dam was taken down in September 2018, it opened up 65 miles of the Patapsco River for fish to travel. This helps fish like alewife, blueback herring, American shad, hickory shad, striped bass, and sea lamprey return to their homes. The American eel, which lives in freshwater and goes to the ocean to breed, will also benefit. This project was led by American Rivers and the Maryland Department of Natural Resources.

If Daniels Dam is also removed, it would help fish travel even further along the Patapsco River and its branches.

Water quality

The eastern part of the Patapsco River is in a busy urban area and faces problems with stormwater runoff and other types of water pollution. The Lower North Branch has high levels of certain heavy metals, phosphorus, fecal coliform bacteria, and PCBs. The Piney Run Reservoir on the South Branch also has too much phosphorus and sediment.

Groups like The Friends of Patapsco Valley & Heritage Greenway help clean up the river. From 2006 to 2012, volunteers removed a lot of trash from the streams in the area.

Recreation

The Patapsco River is a fun place for many outdoor activities. People can swim in certain areas, enjoy rope swings, float down the river on inner tubes, and go rafting. It’s also a great spot for fishing, especially for trout that are stocked by the Maryland Department of Natural Resources in Patapsco State Park each spring. A special kind of fish called the Northern Snakehead now lives in the river, from historic Ellicott City all the way to the harbor.

Crossings

This section lists all the places where roads, bridges, or other paths cross over the main part of the Patapsco River and its two smaller parts, the Middle Branch and Northwest Branch. The list starts from the part closest to the water and moves up to where the river begins.