Lake Petenwell is Wisconsinâs second largest body of water (23,000+ Acres), created by Wisconsin River Power Company in the 1940s by building a Hydroelectric Dam on the Wisconsin River. Lake Petenwell is also known as Petenwell flowage. It has plenty of fine waterfront real estate around Petenwell County Park which is one of Central Wisconsinâs most popular parks. Just south of the Petenwell Dam, is Castle Rock Lake, which is WI 4th largest lake. Theses two lakes, along with the Wisconsin, River separate Adams County & Juneau Cty. Today Lake Petenwell is one of Central Wisconsin biggest attractions along with Wisconsin Dells, which is only about 30 minutes directly south.