The Sonoma County Water Agency expects to impose mandatory water restrictions in four to six weeks, the earliest and most aggressive step the agency has ever taken to combat what is shaping up to be a potentially devastating drought.

The agency will declare this a dry water year on Sunday and will begin reducing the amount of water it releases into the Russian River from Coyote Dam on Lake Mendocino.

Then on Monday, water officials will inform representatives of the agency?s major customers that mandatory water rationing of from 30 percent to 50percent is likely within four to six weeks.

It will be the first time the Water Agency has ever instituted mandatory water rationing, a reflection of just how dire the situation is becoming as the dry winter continues.

?This is most aggressive call in the whole Bay Area, said Brad Sherwood, spokesman for the agency. ?We are completely dependent on Lake Sonoma and Lake Mendocino.?

It will be up to the individual cities and water districts the agency serves to implement conservation efforts. How drastic those plans are remains to be seen. But the agency says it wants the public to be fully aware of what lies ahead.

?We want to be totally transparent,? Sherwood said. ?The last thing we want to do is have people say, ?You didn?t warn us.?

Rainfall in Sonoma and Mendocino counties is less than half of average, providing little inflow into Lake Pillsbury, Lake Mendocino and Lake Sonoma, the primary sources of drinking water for 800,000 people from Ukiah to San Rafael.

Even if there is substantial rainfall, the North Bay may be reclassified as ?critically dry? on March 1, with severe summertime cuts in releases from both Lake Sonoma and Lake Mendocino that will reduce the water flow in the Russian River to 35cubic feet per second.

Those are levels that have not been seen since the drought years in the 1970s.

In comparison, on Thursday the river was running at 276 cubic feet per second.

?You will not be able to take a canoe from Healdsburg to the ocean; you will have to carry it over the sandbars,? said Royce Brooks, who has lived near Odd Fellows Park for 40 years.

It will be the third year that residents will be asked to curtail water use, but this time it will be mandatory and more drastic.

In the past two years, voluntary conservation of 15 percent was achieved to save water in Lake Mendocino to be released in the fall for the salmon run.

The inflow from rain into Lake Pillsbury is the criteria for rating the water year. Since Oct. 1, the inflow has been 23,696acre-feet. A normal year is 39,600acre-feet, and a critically dry year is less than 20,000 acre-feet.

?It is very bad,? said Pam Jeane, deputy chief engineer of operations. ?And truly I hope I can be accused of crying wolf later in the year, that would be just fine with me.?

The lack of rain has left Lake Pillsbury at about 18 percent of capacity, stoking fears by resort owners that no one will want to visit this summer ?to see a mudhole.?

?I don?t want to discourage people from coming up, there are other things to do,? said Mark Parnell, co-owner of Lake Pillsbury Resort. ?There is water, but there is definitely a walk out to the water.?

On Sunday, because of the declaration, the Water Agency will slowly begin reducing the flows from Coyote Dam into the Russian River from 140 cubic feet per second to 75 cubic feet per second, saving about 75 acre-feet of water a day.

The effect on the Russian River will be noticeable mostly in the velocity of the water, said David Manning, a senior environmental specialist.

The changes will be most noticeable in areas that are already shallow, and less noticeable in areas that are wider or deeper, Manning said. ?If it?s a riffle ... it will show up, because riffles are so shallow already; you will see more exposed streambeds,? he said.

?Where you will see the real bad low water is between the outtake at Hacienda to Villa Grande,? said Paul Casini, whose family has had a campground near Duncans Mills since 1883. ?The upper part will go underground, you will see the river go dry.?

River resident Brooks said there is no control over a drought, but he believes that the Water Agency and Sonoma and Marin counties have not adopted strict enough conservation measures.

?We?re in for a deep situation until we get rain, and it doesn?t look like we will get rain this year,? Brooks said. ?But we are slow to react.?

You can reach staff writers Kevin McCallum at 521-5207 or kevin.mccallum.com and Bob Norberg at 521-5206 or bob.norberg@pressdemocrat.com.