Winnisquam Lake is located in Belknap County in central New Hampshire, in the communities of Meredith, Laconia, Sanbornton, Belmont, and Tilton. At 4,238 acres (1,715 ha), it is the fourth-largest lake located entirely in New Hampshire. The lake is primarily fed by the outlet from Lake Winnipesaukee, and Winnisquam's outlet is the Winnipesaukee River, flowing to the Merrimack River. The lake has a maximum depth of 170 feet (52 m).

Winnisquam Lake is home to many species of fish. Cold water species include brook trout, rainbow trout, brown trout, lake trout, landlocked salmon, and whitefish. The warm water species include small- and largemouth bass, pickerel, horned pout, white perch, northern pike, walleye, black crappie, bluegill, and yellow perch. Remote lake and brook trout stocking is common when authorities find it necessary.