Lake Decatur is a man-made reservoir located in Decatur, Illinois. It was created in the 1920s by damming the Sangamon River and serves as a primary water supply for the city. The lake covers approximately 2,800 acres and has a maximum depth of around 30 feet. The lake is popular for recreational activities such as fishing, boating, and swimming. It is home to various fish species, including largemouth bass and bluegill. Surrounding the lake are parks and trails, making it a favored spot for outdoor enthusiasts and families.