The Hammonasset River is formed about 4 miles (6.4 km) southeast of Durham, Connecticut along a gully on the north end of Bunker Hill at about a half mile northeast of the junction of Route 148 and Bunker Hill Road. The river travels for 21.0 miles (33.8 km) to Clinton Harbor on Long Island Sound just east of Hammonasset Beach State Park. A popular paddling route runs for about 10 miles (16 km) starting along Summer Hill Road about 2.5 miles (4.0 km) south on Route 79 from North Madison, Connecticut.