615 ILCS 5/7
It shall be the duty of the Department of Natural Resources to have a general supervision of every body of water within the State of Illinois, wherein the State or the people of the State have any rights or interests, whether the same be lakes or rivers, and at all times to exercise a vigilant care to see that none of said bodies of water are encroached upon, or wrongfully seized or used by any private interest in any way, except as may be provided by law and then only after permission shall be given by said department, and from time to time for that purpose, to make accurate surveys of the shores of said lakes and rivers, and to jealously guard the same in order that the true and natural conditions thereof may not be wrongfully and improperly changed to the detriment and injury of the State of Illinois.
In order to expedite the fulfillment of such duties by the department, and to remove or reduce many causes of contention between the State and riparian owners, every subdivision plat drawn for any land bordering or including any public waters of the State of Illinois in which the State has any property rights or property interests, shall be submitted to the Department of Natural Resources for review and approval as to the boundary line between private interest and public interests, and shall not be recorded until so reviewed and approved by the department. Should the department find such boundary line to be incorrectly indicated on the plat, it shall return the plat unapproved with a statement in detail of the reasons for not approving such plat.
The Department of Natural Resources shall have power and authority to inquire into encroachments upon, wrongful invasion and private use of every stream, river, lake or other body of water in which the State of Illinois has any right or interests. The department shall have power to make and enforce such orders as will secure every stream, river, lake or other body of water, in which the State of Illinois has any right or interest against encroachment, wrongful seizure or private use.
615 ILCS 5/7