The Coonamesset River (or Coonamessett River on federal maps) is a 3.1-mile-long (5.0 km) river in Falmouth, Massachusetts on Cape Cod. The river has its headwaters in Coonamessett Pond, flows generally south to Great Pond estuary, and empties into the Vineyard Sound just east of Falmouth Heights. The river is shallow running through old glacial deposits of sand and gravel, and hosts a major New England herring run. Red maple swamps border the river along its headwaters and at its mouth where it runs through private property and Town land, while along the lower river it is largely flanked by commercial cranberry bogs that run to the rivers edge.