615 ILCS 5/26
The Department of Natural Resources shall, for the purpose of protecting the rights and interests of the State of Illinois, or the citizens of the State of Illinois, have full and complete jurisdiction of every public body of water in the State of Illinois, subject only to the paramount authority of the Government of the United States with reference to the navigation of such stream or streams, and the laws of Illinois, but nothing in this Act contained shall be construed or held to be any impairment whatsoever of the rights of the citizens of the State of Illinois to fully and in a proper manner, enjoy the use of any and all of the public waters of the State of Illinois, and the jurisdiction of the Department of Natural Resources shall be deemed to be for the purpose of protecting the rights of the people of the State in the full and free enjoyment of all such bodies of water, and for the purpose of preventing unlawful and improper encroachment upon the same, or impairment of the rights of the people with reference thereto, and every proper use which the people may make of the public rivers and streams and lakes of the State of Illinois shall be aided, assisted, encouraged and protected by the Department of Natural Resources.
615 ILCS 5/26