Salvinia effort has cleared 75 percent of Lake Wilson

By Catherine E. Toth
Advertiser Central O'ahu Writer

WAHIAWA — Suddenly, 75 percent of Lake Wilson has been cleared of the noxious Salvinia molesta weed, and officials are talking about 90 percent by the end of the month.

About 500 tons of fish survived the salvinia threat at Lake Wilson, where oxygen levels have improved dramatically. Eugene Tanner • The Honolulu Advertiser

The state's fight started with disappointingly slow progress, and by last week only about 30 percent of the lake had been cleared.

But following a steep learning curve in the early weeks, the effort began to gain momentum — so much that even state officials were surprised to hear that three-quarters of the lake had been cleared.

"I told my guys, 'You're kidding me,'" said Eric Hirano, head of engineering for the state Department of Land and Natural Resources. "I had to go down on Tuesday to see it for myself."

Oxygen levels in the lake have improved dramatically, with plankton growing back and enough cleared water to allow for oxygen exchange. About 500 tons of fish, including largemouth bass, survived the salvinia threat.

Officials even hope to open the lake to fishing soon.

It's a far cry from the situation seven weeks ago, when the extraction effort began with one site and a handful of workers.

Realizing the scope of the problem, officials quickly ramped up the fight against the aggressive weed, which can produce up to 400 tons of new growth per day.

"It was overwhelming at first," said Glenn Higashi, an aquatic biologist with the Division of Aquatics Resources who has coordinated cleanup efforts since extraction began. "But I thought it was possible ... If I wasn't optimistic, I would've quit a long time ago."

More than $1 million was pledged to the fight, and an interagency effort was created to coordinate city, state and military crews pulling salvinia by machine and hand, a number of extraction sites and the use of an aquatic herbicide.

"We wouldn't have had a prayer (without the herbicide)," Hirano said.

The herbicide stopped the weed from multiplying. The sprayed salvinia shrank and turned brown, making removal easier. Some of the dead plants sank.

Crews figured out the best approaches and techniques to remove the weed, and after a few weeks, "we just started cranking," Hirano said.

"Our goal was to save the lake and avoid a public health disaster," Hirano said. "We just kept pushing to get the job done as quickly as possible."

Today, most of the salvinia has been extracted from four sites, with more than 40 people, including military volunteers, working almost every day. The remaining weeds cling to the edges of the lake or are in areas that larger boats can't get to.

Currently, the state operates one site on the peninsula at the end of Malulu Place with two excavators, and the city runs another behind the Kemo'o By The Lake condominiums on Wilikina Drive.

The U.S. Army will close its site on the north side of the lake. There's nothing left to extract there.

The lake has returned to its emerald green. Schools of peacock bass and tilapia skirt beneath the surface. It's finally starting to look like the quiet, peaceful lake that Wahiawa residents remember.

The Lake Wilson Recreation Area remains closed, and getting the lake 90 percent free of salvinia is the short-term goal.

The state, despite its efforts, will never get rid of the invasive weed.

"It's not possible to completely eradicate it," said Randy Honebrink, education coordinator for the Department of Land and Natural Resources' Division of Aquatic Resources. "It will always grow back again. And we'll always have to be there, surveying the lake, spraying herbicide, getting rid of it. It will take a lot of effort over a long period of time."