A chemical will be used for the first time in Lake Tapps to battle the annoying and sometimes dangerous growth of Eurasian milfoil.
On Aug. 30 -31, a contractor will spread about 200 pounds of fluridone in pellet form over 400 acres where the invasive underwater plant is most heavily concentrated in the 2,700-acre lake.
It will be the first of three applications of the herbicide by Cascade Water Alliance, the consortium of King County cities and water districts that owns and manages the East Pierce County lake. The second treatment will follow in two weeks and the last in six weeks.
No swimming or fishing restrictions are planned. The chemical is safe for humans at the levels being applied in the lake, according to the state Department of Health.
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It’s even safe enough to drink, according to Cascade, although the consortium doesn’t plan to use the lake for that purpose for decades.
The federal Environmental Protection Agency has set an acceptable standard for fluridone in drinking water at 150 parts per billion. The level in Lake Tapps will be between 8 and 20 parts per billion, according to Cascade.
The contractor’s goal is to eradicate from 65 percent to 90 percent of the milfoil by next season, said Jon Shimada , the consortium’s director of capital projects.
Chuck Romeo, president of the Lake Tapps Community Council, was guardedly optimistic about the plan. The council represents more than 2,000 lakeside homeowners.
“It looks pretty good,” Romeo said. “We’ve had quite a few meetings on it.
“Something is better than nothing.”
Romeo said there isn’t much milfoil where he lives at Driftwood Point, but “Snag Island is pathetic. You can’t run a boat through it.”
In response to residents’ complaints about the noxious weed, Cascade held three public meetings. A consultant was hired to survey the lake and pinpoint the worst areas.
Cascade, which bought the lake in 2008, is spending $340,000 on the three applications.
Shimada said the herbicide treatments mark the beginning of a five-year plan proposed by the consultant and adopted by Cascade to monitor and control the weed.
Eurasian milfoil can grow into dense underwater mats. It not only affects the health of other native aquatic plants, it can be dangerous to swimmers who get caught in it. It can foul boat propellers and degrade fish habitat.
A non-native plant, it is usually transmitted around the state by visiting boats.
Shimada said lake users and residents won’t notice much change this year; it will take up to 90 days to start seeing the milfoil die.
The amount of milfoil has increased in the last few years, he said. Warm, slow-moving water and sunlight are prime ingredients to grow the plant.
Shimada said there’s some speculation that when longtime owner Puget Sound Energy used the lake as a reservoir to run its White River power station, river water flowed more quickly through Lake Tapps. It also was murky because the water was glacier-fed, so there was less sunlight to help the plant grow.
Since the power station closed in 2004, he said, the lake water has become clearer and warmer. The lake level also stays higher all year long.
Fliers announcing the upcoming chemical applications are being delivered door to door. Shimada said fliers also will be posted on lakefront docks.
Affected residents will get a reminder notification on their property 24 hours before each application.