Indiana has approximately 21,000 miles of rivers and over 450 natural lakes, according to the Indiana Department of Natural Resources. The Hoosier State also has 580 impoundment lakes, or man-made reservoirs. These reservoirs were created to prevent flooding from Indiana's rivers. As of May 2011, the state of Indiana provides 366 sites on lakes and rivers that allow public boating and fishing.
The longest river that passes through Indiana is the Ohio River, which runs past the state's southern border. This 981-mile river is the longest tributary of the Mississippi River. The Ohio River also has its own tributaries, such as the Wabash River, Anderson River and Whitewater River. The Wabash River, Indiana's official state river, is the longest instate river at 491 miles. Northern Indiana is home to the Maumee River, which starts at Fort Wayne and reaches Lake Erie near Toledo, Ohio. Some Indiana rivers have their mouths at Lake Michigan, such as St. Joseph River, Galena River and Grand Calumet River.
The largest lake in Indiana is Lake Monroe at 10,750 acres. Lake Monroe is within 30 minutes of Bloomington, home to the University of Indiana. This lake is also surrounded by the 13,000-acre Brown County State Park. Other large impounded lakes in Indiana include the 8,800-acre Patoka Lake in Hoosier National Forest and Mississenewa Lake – a 3,180-acre body of water in north central Indiana. Lake Freeman and Lake Shafer are two impounded lakes connected to each other in northern Indiana; these two lakes are home to Indiana Beach, a tourist destination.
At 3,500 acres, the largest natural lake in Indiana is Lake Wawasee, which is in north central Indiana by the city of Syracuse. Other notable Indiana natural lakes are the 1,229-acre Lake James, 585-acre Webster Lake and 880-acre Tippecanoe Lake. Tippecanoe Lake is Indiana's deepest natural lake with a maximum depth of 123 feet. Nearly all of Indiana's large natural lakes are in the northern part of the state. According to Indiana University, Indiana's natural lakes were formed from melted glacial ice settling into deep depressions in the state's landscape.
Some of Indiana's northwest border is on the shores of Lake Michigan, the third largest of the Great Lakes. Lake Michigan is also the sixth largest freshwater lake in the world, with a total water surface area of 22,300 square miles. Most of northern Indiana's shoreline on Lake Michigan is a part of the Indiana Dunes National Lakeshore, which serves as a wildlife refuge. Two of Indiana's cities, Gary and Michigan City, are waterfront cities on Lake Michigan.