Crystal Lake is a 441-acre (1.8 km) water body located in Belknap County in the Lakes Region of central New Hampshire, United States, in the town of Gilmanton. Water from Crystal Lake flows via the Suncook River to the Merrimack River.
Near Gilmanton Iron Works is primarily a warm water fishery but, has been stocked with the cold water species Rainbow Trout in recent years. It has a rocky bottom, an extensive shoal area, and an abundance of surface vegetation. The shoreline is heavily wooded and moderately developed with camps. A fre, state owned launch site at the southern tip provides good access.