Cal. Code Regs. tit. 23 § 3939.34
Los Angeles Regional Water Quality Control Board (Los Angeles Water Board) Resolution No. R4-2007-018, adopted on November 1, 2007 by the Los Angeles Water Board and approved by the State Water Resources Control Board on October 21, 2008 under Resolution No. 2008-0076, modified the regulatory provisions of the Water Quality Control Plan for the Los Angeles Region (Basin Plan) by subdividing Reach 4 of the Santa Clara River as two separate Reaches: Reach 4A between the confluence of Piru Creek and the A Street Bridge in the City of Fillmore, and Reach 4B between the Blue Cut Gauging Station and the confluence of Piru Creek. This action is based on current understanding of the water quality differences between the western and eastern portions of Reach 4 due to the significant alterations to land uses and waste discharges within the Upper Santa Clara River watershed.
Cal. Code Regs. Tit. 23, § 3939.34