Flat Lake   Be the first to submit input for Flat Lake. If you have info on Flat Lake, Campbell County, South Dakota please submit it here to improve this web site.          These outdoors activities are available near Flat Lake.   Lakes Near Flat Lake: Swan Lake, Walworth County, 19 miles away   Public Lands Near Flat Lake: Lake Hiddenwood Recreation Area, South Dakota, 15 miles away Doyle Memorial State Park, North Dakota, 33 miles away Beaver Lake State Park, North Dakota, 37 miles away