Rosillo Creek and portions of Leon, Olmos, and Salado Creeks and their respective watersheds and defined by Exhibit 2, a part of Ordinance 38511 of the City of San Antonio dated May 7, 1970, an area lying wholly within Bexar County, Texas, is designated as an area which the development and use of regional and area-wide waste collection, treatment, and disposal systems are necessary and desirable in order to prevent pollution and maintain and enhance the quality of the waters in the state.