'Definite success' seen at Lake Wilson
By Zenaida Serrano Espanol
Advertiser Staff Writer
Herbicide sprayings of Salvinia molesta at Lake Wilson are helping removal efforts, with noticeable areas of the lake clearing as the treated weeds die and sink to the bottom, state officials said.
Deborah Booker • The Honolulu Advertiser
State Department of Agriculture workers have been spraying the AquaMaster herbicide over Lake Wilson's 300 acres for three weeks, completing the first of two phases on Friday. Officials sprayed 214 acres of the lake during the first two weeks, and 175 acres during the third week.
Herbicide spraying causes the Salvinia molesta to decompose and sink. In this photo of Lake Wilson, taken yesterday, treated plants are brown; they should start to sink by mid-April, said Larry Nakahara of the Department of Agriculture.
Tony Montgomery, aquatic biologist with the state Department of Land and Natural Resources' Division of Aquatic Resources, visited the lake yesterday and saw "definite success."
"Certain areas are clearing out and the south fork ... has a tremendous amount of clear water," Montgomery said.
Department of Agriculture workers are ahead of their planned schedule of spraying 50 acres a week because of improved techniques and modified equipment, said Larry Nakahara, the department's plant pest-control manager.
"Our primary objective was to treat the plants so that they would eventually die and sink and thereby free up the surface of the water so that the oxygen can ... permeate throughout the water source to prevent these massive fish kills that people were trying to avoid," Nakahara said.
He described AquaMaster as "a very safe pesticide."
Of the commercial herbicides tested by the U.S. Army Corps of Engineers that are approved for use for aquatic weed control by the U.S. Environmental Protection Agency, AquaMaster was one of the most effective.
The second and final phase of the project will begin in two weeks, Nakahara said.
"The treated plants (from the first phase) will be dark brown and places that we missed for whatever reason will still be green, so with the second phase, the plan is to go in and finish those off," he said. "We expect to see the salvinia start sinking into the water about mid-April."
The decomposing plants that sink to the bottom of the lake will deplete oxygen and possibly kill some fish, Nakahara said, "but the notion was it was more important to free up that surface area to make it available for an exchange of oxygen."
As of Saturday, city, state and military workers had removed 19,189 cubic yards of the weed since extraction efforts began Feb. 20. That work will continue, state officials said.
But Wahiawa resident John Lopez is skeptical.
"When (workers) came Saturday, they did a big area, but this morning, it was all covered up again," Lopez said. "If they miss one day, it'll cover up again."
Reach Zenaida Serrano Espanol at zespanol@honoluluadvertiser.com or 535-8174.
