70 ILCS 1205/11-2
When any park district borders upon any navigable body of water, the title to the bed or submerged land of which is vested in the State of Illinois, said district may take possession of, enclose, fill in, reclaim and protect any portion of such submerged land bordering thereon, over which there shall be shoal and shallow water not fit for navigation and shall have the power to establish, construct and maintain parks and boulevards over and upon the same, and all right, title and interest of the State of Illinois in and to the bed or submerged land of such body of water so taken possession of, enclosed, filled in and reclaimed is hereby granted and ceded to such park district and the title thereto shall vest in such park district to be held for the use and benefit of the public as a part of said park district for park and boulevard purposes exclusively, and said district shall have power for the purpose of reclaiming such submerged land and protecting the same thereafter, to construct all necessary break-waters, or protection for the building and maintenance of such parks and boulevards, and the enclosing or reclamation of such submerged lands.
Any such submerged lands so enclosed and reclaimed as aforesaid shall forever be held and maintained for park and boulevard purposes and no portion thereof shall ever be granted or ceded away by any district for any purpose, and in case the same should ever cease to be used for park or boulevard purposes, then the title to the same shall revest in the State of Illinois, together with all the improvements thereon and the appurtenances thereof.
70 ILCS 1205/11-2