State authorities Thursday began notifying hundreds of water rights holders on the upper Russian River to stop diverting water from the drought-stricken watershed because there isn't enough supply to go around.
The unprecedented step affects 652 water rights issued after Feb. 19, 1954, held by dozens of growers and local water agencies, some of which rely on the river for their main supply. Many have other sources, however, that could help protect them through the dry season.
The order, which was dated Wednesday and takes effect immediately, was issued in letters sent out by the state Water Resources Control Board.
"Based upon the most recent reservoir storage and inflow projections, along with forecasts for future precipitation events, the state Water Board has determined that the existing water supply in the Russian River watershed is insufficient to meet the needs of all water rights holders," the state agency said in its letter.
The upper Russian River is the portion between Lake Mendocino and the river's confluence with Dry Creek near Healdsburg. The lower Russian River, which is fed by Lake Sonoma, is not affected by the order.
The move by the state is aimed at preserving supplies for senior water rights holders in the watershed, said George Kostyrko, public affairs director for the state Water Resources Control Board.
It follows similar action taken by the state to curtail diversions in the Sacramento River watershed and on the Scott River in Siskiyou County. It is the first such move on the Russian River.
Most of the affected users are farmers and agencies that provide drinking water. Many hold multiple rights, so the impacts of the order are not entirely clear. State law also prioritizes deliveries of drinking water, so municipal supplies are not set to be halted by the action but could be reduced as a result.
Most water agencies in the region already are urging or requiring cuts of 20 to 25 percent from domestic users.
The order does not affect water already impounded in privately owned reservoirs or in Lake Mendocino, built in the late 1950s.