Larvae, Algae Force Closure of Reservoir : Pollution: No health risk seen in their presence in Silver Lake waters. Reopening is scheduled in two weeks.

Reports of tiny brown wormlike larvae spotted in glasses of water and bathtubs just south and west of downtown Los Angeles triggered the temporary closure Wednesday of the Silver Lake Reservoir.

Though harmless, the midge fly larvae--coupled with a slight green tint and musty odor from unusually high algae levels in the reservoir--made the drinking water less than appealing, Department of Water and Power officials said in explaining their decision to shut the 77-acre reservoir for at least two weeks.

“While there is no health risk with midge fly larvae, they are admittedly aesthetically unpleasant,” said James F. Wickser, DWP assistant general manager for water.

“So there’s no cause for alarm now,” said Bob DiPrimio, a sanitary engineer with the DWP’s water quality division.

He added that it will take two to three weeks to superchlorinate the reservoir to kill the larvae hatched from midge fly eggs and clear away the algae that have given the usually crystal-blue lake a greenish hue.

Alternate sources will be used to supply water to the affected areas in the meantime.

Complaints from eight customers during the past week about the quarter-inch or longer, thread-like organisms in their drinking water were enough to trigger the closure.

DWP officials said that several hundred thousand customers might be affected. The area served by the reservoir is bounded by Beverly Boulevard on the north, Vernon Avenue on the south, Western Avenue on the west and Central Avenue on the east.

The Silver Lake community itself is served by the much smaller Ivanhoe Reservoir that adjoins Silver Lake Reservoir.

Clouds of small midge flies, common spring and summertime visitors to standing bodies of water, are usually kept under control by spraying vegetation surrounding the reservoirs, officials said.

Despite aggressive measures taken to maintain water quality, “sometimes Mother Nature has better plans than we do,” DiPrimio said.

Unusually high numbers of midge flies found recently in DWP traps placed around Silver Lake Reservoir were the first indication that this might be an unusual summer, DiPrimio said.

A number of factors, such as weather, water temperature and the extent of spraying, can affect the fly population and reproductive cycle, the DWP engineer said. While spraying to kill the insects was done about three weeks ago, it may have been too late, he speculated, adding that the flies may have already laid their eggs on the water’s surface by then.

Most summers, the DWP gets only a handful of midge fly larvae sightings from throughout its service area. This time, it got eight calls from the same area and all within a week. The DWP usually deals with the problem by flushing out water mains and pipes in the specific areas where the larvae are spotted.

But this time the infestation, coupled with the unusually high level of algae growth--which DiPrimio called “the more serious problem”--made the shutdown imperative.

The algae had reduced water quality beyond acceptable levels, he said. It had proliferated beyond the level where it could be controlled with normal chlorine treatment and the reservoir had to be shut down to “shock treat” it with larger chlorine doses, he said.

Overgrown algae is a common problem in open reservoirs where sunlight contributes to its proliferation.

Noting that the larvae and algae are endemic to open, standing bodies of water, DiPrimio said that “as long as we have open reservoir systems, we are going to have these problems from time to time.”