Swains Lake (also known as Union Lake) is a water body located in Strafford County in eastern New Hampshire, United States, in the town of Barrington. Water from Swains Lake flows via the Bellamy River to the Piscataqua Riverestuary. A boat launch is available off Young Road. During the spring and summer it is a popular boating destination, while the ice of the colder months connects several snowmobile paths.