State regulators want to leave more water for fish and wildlife in the heavily tapped tributaries of the San Joaquin River, setting the stage for another bruising California water fight. The proposal to keep more water flowing in the Merced, Tuolumne and Stanislaus rivers could spread the pain caused by environmentally related water cuts to irrigation districts and cities that have largely escaped them, thanks to their location and seniority in the hierarchy by which the state allocates water rights.