The Gunpowder River is a 6.8-mile-long (10.9 km)[1] tidal inlet on the western side of the Chesapeake Bay in Maryland, United States.

The Big Gunpowder, 56.7 miles (91.2 km) long,[1] begins in the extreme southern part of Pennsylvania's York County.

The nearby site of old Joppa was an important deep-water seaport, and rival to the port of Baltimore, in colonial American times, until sedimentation of the Gunpowder River -- caused by upstream development[citation needed] -- made its harbor inaccessible to large ships.

Nonetheless, Gunpowder State Park on the Chesapeake Bay may give one the impression that this is still a somewhat remote river.

Both streams flow over the Fall Line separating the Piedmont Plateau from the Atlantic Coastal Plain just downstream of US Route 1.