Caddo Lake National Heritage Area Act of 2018 This bill establishes the Caddo Lake National Heritage Area in Louisiana and Texas. The bill designates the Caddo Lake Heritage Area Commission as the management entity for the area. The commission shall submit a management plan for the area. Such plan must contain an inventory of the cultural, natural, historical, educational, scenic, and recreational resources in the area, including a list of the property that is related to the area's themes and that should be conserved, enhanced, managed, or developed.