The San Gabriel River Watermaster (Watermaster) administers the Los Angeles County Superior Court Judgment “Board of Water Commissioners of the City of Long Beach, et al vs. San Gabriel Valley Water Company, et al”, which is informally known as “The Long Beach Judgment”.  This Judgment regulates the amount and distribution of surface water and groundwater flowing from the San Gabriel Valley in the north (Upper Area) through the Whittier Narrows and into the Central Basin in the south (Lower Area).  The Long Beach Judgment established a physical solution for a fair division of the water supply of the San Gabriel River System between the Upper Area and Lower Area in accordance with the Court’s orders and has been effective in doing so since its adoption on September 24, 1965.

The Watermaster is comprised of three persons appointed by the Los Angeles County Superior Court to administer and enforce the provisions of the Long Beach Judgment.  The detailed operations described in the Long Beach Judgment are complex and require continuous compilation of data so that annual determinations can be made to ensure compliance with the Long Beach Judgment. 

The Watermaster collects data on streamflow, rainfall, water quality, groundwater levels, subsurface flows, exported water through the Whittier Narrows, recycled water, imported replenishment water, and other information as required to determine factors such as the Lower Area Entitlement, Usable Water received by the Lower Area, Upper Area credits or debits, and any make-up water requirements.  Details of Watermaster activities can be found in the Annual Reports and in the Judgment.