The Patapsco is a river in central and coastal Maryland. While it begins at the confluence of two named branches approximately 50 miles inland, it is a minor river for most of its length; however, its last 10 miles are a large tidal estuary inlet of Chesapeake Bay. The inner part of this estuary provides the harbor of Baltimore, comprised of the Northwest Harbor and the Middle Branch. (See Baltimore Inner Harbor.) Another inlet, to the south, is Curtis Bay. It is located south of the Back River, sometimes considered part of the Patapsco River watershed, and north of the Magothy River. The next river north of the Back River is the Middle River.

It has a watershed area (including the water surface) of 680 square miles, or 632 square miles of land. Thus, its total watershed area is 7% water. Patapsco Valley State Park is adjacent to 32 miles of the Patapsco, encompassing a total of 14,000 acres in five different areas.

The tidal Patapsco is crossed by two tunnels and several bridges, notably the Baltimore Harbor Tunnel (Interstate 895), the Fort McHenry Tunnel (Interstate 95), and the Francis Scott Key Bridge (Interstate 695). Notable railway bridges include the Thomas Viaduct and the ruins of the Patterson Viaduct.

References

• Chesapeake Bay Program Watershed Profile: Patapsco/Back River
• Patapsco Valley State Park

Further reading

• Maryland DNR's Surf Your Watershed: Patapsco/Back River
• Maryland Port Administration
• Patapsco Riverkeeper

Chesapeake Bay Watershed | Rivers of Maryland