Bass River is an estuary and village in South Yarmouth, Massachusetts, United States. The estuary separates the towns of Yarmouth and Dennis at the central, southern sections of the towns. At its widest and most southerly point, it opens to and meets Nantucket Sound. Its brackish, northwestern end flows into Follins Pond, from there winding further north as a brook, then an underground stream that nearly bisects Cape Cod. The mouth of the river is between Smugglers Beach on the Yarmouth side and West Dennis Beach on the Dennis side. West Dennis beach has become a popular site for kite boarding in the past few years. In the same way Kalmus Beach in Hyannis has become popular for windsurfing. Once inside the river, there is a large land mass covered with sea grass in the middle of which is a large bay. The island is called 'Grass Island' by the locals. Grass Island separates Bass River into two parts. The right side of the river goes towards West Dennis and the Fingers development. The left side is the main branch of the river passing Windmill Beach, Bass River Yacht Club, and Shipshops Marina. After the marina, the river goes under a large bridge and continues deep into the cape. Bass River is home to a friendly rivalry between West Dennis Yacht Club and the Bass River Yacht Club. These clubs also compete against Hyannis Yacht Club, Wianno Yacht Club, and others in the Southern Massachusetts Sailing Association team racing circuit. The Yarmouth shores are home to Bass River Golf Course, which is owned and operated by the town of Yarmouth.