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On the surface, Lake Mendocino appears to have plenty of water, especially when compared with the near-record low levels that turned most of the lake into a mudflat last year. But the lake’s water level already has begun a steady decline that has farmers and water officials concerned it could again shrink to near empty by the end of this fourth year of drought.

“Everybody’s watching it,” Mendocino County Farm Bureau Executive Director Devon Jones said.

Unless significant rain falls this spring, state regulators are likely to repeat last year’s unprecedented curtailment of hundreds of water rights held by farmers and others along the Russian River between Lake Mendocino and Healdsburg.

The state already has curtailed water rights to some Sacramento River tributaries and notified Russian River water users they could be next. State officials also have extended mandated water restrictions for all domestic uses in California.

“I expect they’ll be seeking curtailments again” on the upper Russian River, said Alfred White, a viticulturist and member of the Russian River Flood Control and Water Conservation Improvement District, which holds Mendocino County’s right to 8,000 acre-feet of water in Lake Mendocino.

Lake Mendocino appeared headed for normal water levels following early winter storms, but then the rain tapered off, followed by the end of a regulatory effort to conserve that water.

The water level began dropping in mid-February, just after the expiration of a state-issued variance that temporarily reduced the minimum in-stream flows in the Russian River between Lake Mendocino and Healdsburg. The flows, aimed largely at preserving fish, are managed by the Sonoma County Water Agency, except when there’s a risk of flooding.

Between midday Thursday and midday Friday, the lake lost 247 acre-feet of water. An acre-foot is roughly enough to fill a football field with one foot of water or supply one household with 893 gallons of water a day for a year.

Under the now-expired variance, the upper Russian River’s minimum in-stream flow requirements were reduced to 50 cubic feet per second. When it expired Feb. 20, the flow requirements tripled to 150 cfs, said Pam Jeane, assistant general manager of the Sonoma County Water Agency. On Friday, water was being released from Coyote Dam at a rate of 119 cfs to keep up with the river flow requirements.

Since the lake releases were increased, Lake Mendocino has declined from about 70,000 acre-feet to 65,546 acre-feet of water, about 59 percent of its maximum water supply pool and about 83 percent of the current allowed water supply pool. The amount of water allowed to be stored in the lake varies, depending on the time of year, with less allowed during the winter when rains could cause flooding.

The current lake level would not be a problem if plenty of rain was assured later this year. But four years of drought have proven it’s unwise to count on that happening.

The speed at which the lake declines will escalate next month unless additional regulatory variances are granted by the state or it rains. The National Weather Service said there appears to be precipitation on the horizon, but it’s too early to tell whether it will be significant.

The minimum Russian River flows are scheduled to increase to 185 cfs at the end of March, Jeane said. She said the agency likely will petition for some type of variance to the water release rules by May.

Local officials would like to see Sonoma County petition for another change in the flow regimen before the lake loses much more water.

“Sooner than later,” the farm bureau’s Jones said.

The Water Agency has petitioned for changes in the water flow regulations three times in two years because of the ongoing drought, Jeane said. Between the variances and water conservation efforts, she estimated 25,000 to 30,000 acre-feet of water has been saved.

That helps, but it’s not a long-term solution, viticulturist White said.

“We need to raise the dam” so it can hold a two-year supply of water rather than just one, he said.

Mendocino County officials have been promoting that proposal to the Army Corps of Engineers for decades, but so far it has failed to progress beyond some cursory studies.

Local officials also are pursuing legislative changes that would allow more flexibility in managing the winter water storage in Lake Mendocino and, theoretically, avoid letting water out of the dam unnecessarily.

You can reach Staff Writer Glenda Anderson at 462-6473 or glenda.anderson@pressdemocrat.com. On Twitter @MendoReporter.

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