The Eightmile River has its source along a small drainage into several small swamps in an undeveloped region about three miles east of Bashan in the town of East Haddam, Connecticut. This source is fairly centered between Ackley Road, Hall Kilbourne Road, Usher Swamp Road, and Miles Standish Road. The Eightmile River runs for 13.4 miles (21.6 km)[1] to Hamburg Cove near Hamburg, Connecticut.
The East Branch begins 1/10 of a mile west of the junction of Route 85 and Witch Meadow Road, which is about 1 mile north of Salem, Connecticut. A popular paddling route begins about 3 miles southwest of Salem along Darling Road about a half mile southwest of the junction of White Birch Road. Most of the route is whitewater reaching Class III-IV at its most difficult with some flatwater and quickwater between the rapids. A take-out can be reached at the Route 156 bridge just before the river's confluence with the main flow of the Eightmile River.