Santa Clarita / Antelope Valley : Algae Treatment Closes Reservoir for Recreation Until Noon Today : Water: Complaints about a strange taste and smell have led officials to try to rid Castaic’s upper lake of geosmin.

State water officials will close Castaic Lake’s main reservoir to the public until noon today while they treat the lake for algae that have given an unpleasant taste to the drinking water it provides to parts of Los Angeles and Ventura counties.

Helicopter crews will dump 16,000 pounds of copper sulfate into the lake in hopes of removing a musty taste and odor that some water customers have complained about.

High temperatures and abundant nutrients in the water have spurred the growth of algae, known as geosmin, which aren’t dangerous but produce the foul taste and smell.

Treating the lake isn’t expected to solve that problem completely. But the goal is to kill as much of the algae as possible.

“Unfortunately, geosmin cannot be removed from water during the filtration process and Castaic Lake is too large--and the algae too widespread--to attempt to eradicate it in the reservoir,” said Mark Beuhler, water quality director for the Metropolitan Water District.

The reservoir, or upper lake, was treated with copper sulfate in 1973.

The MWD and California Department of Water Resources requested the temporary lake closure. Officials from both agencies say the water is safe to drink even with the algae, even if it doesn’t smell or taste very good.

Tens of thousands of Southern California residents receive a portion of their drinking water from Castaic Lake. The Metropolitan Water District draws water from the Castaic reservoir and the Colorado River, in turn providing it to 27 water agencies that include city, county and municipal water districts in Los Angeles and Ventura counties.

Closing the lake to the public for only a few hours will still have a “significant impact” on the 2,500 people who use the upper lake area daily for fishing, boating, water-skiing and jet-skiing, said Brian Roney, acting superintendent of the Castaic Lake Recreation Area.

Roney said three-fourths of those who use the lake normally come early in the day.

Lake officials balked at earlier MWD plans to shut down the reservoir last Friday, leading into the busy Fourth of July weekend, Roney said.

Representatives from the water agencies are unsure if they will need to close the lake again soon for additional treatment.

“It’s just a natural phenomenon,” said Roseanne Danyluk, public information officer for the Department of Water Resources. “I don’t think it’s something we can predict.”