Quail Creek State Park, Utah

Fed by a pipeline diverting the Virgin River, this 600-acre reservoir just north of St. George holds some of the warmest water in Utah, staying swimmable from May through October even as depths plunge to 120 feet. Boaters, water skiers, and scuba divers share the lake with anglers chasing largemouth bass, crappie, and rainbow trout beneath the surrounding red-rock hills.