DEAN SENSUI / DSENSUI@STARBULLETIN.COM
A City and County amphibious excavator, operated by heavy equipment operator Allen Kaaihue, used its shovel yesterday to help pull its way through the heavy salvinia growth in Lake Wilson.
The Green Monster If ever there were a perfect environment for Salvinia molesta to grow and prosper, Oahu's Lake Wilson is it, mainland experts said yesterday after seeing the green-carpeted water.
City, state and federal officials
Lake Facts
coordinate efforts to remove
a weed covering the surface
of Lake Wilson
By Diana Leone
dleone@starbulletin.comThe aquatic fern likes plenty of sunlight. Check.
It likes nutrient-rich water. With runoff from agricultural fields, residential neighborhoods, with septic tanks, and 3.2 million gallons per day of treated sewage from Wahiawa Wastewater Treatment Plant all coming into the lake, check.
No predators. Check.
Meanwhile, things that kill salvinia, freezing temperatures and salt water, are absent.
Another way to kill it is scooping it out. Work began yesterday with a city excavator scooping plants near the dam end of the lake.
Peter Young, director of the state Department of Land and Natural Resources, said yesterday that there will be operations at four or five sites. Each will use boats and oil booms to pull plants from mid-lake, an excavator to scoop them ashore and three dump trucks to transport the dried plants to a mulching area on Dole Hawaii farmland.
Wahiawa State Freshwater Park, the second site, will be closed soon and remain closed for several months to stage work near its boat ramp.
Michael Grodowitz and four other specialists with the U.S. Army Corps of Engineers are on Oahu three days to share their experience with controlling salvinia in other places and suggestions for attacking it here.
"This is the best-looking salvinia I've ever seen," exclaimed insect specialist Grodowitz, holding up a clump of the furry-leaved floating plant.
Because there is no "magic bullet" to wipe it out, the plant will have to be attacked on several fronts, the group said.
As they stood alongside the 300-acre lake yesterday morning, the scientists reviewed ways to beat salvinia, while admitting they know some may be impractical here.
DEAN SENSUI / DSENSUI@STARBULLETIN.COM
State officials and the Army Corps of Engineers gathered at Wahiawa State Freshwater Park to plan ways of removing salvinia from Lake Wilson.
Suggestion: The lake could be drained long enough for the plant to die from lack of water, then refilled.
Local response: No way. Dole Hawaii uses 14 million to 15 million gallons a day of the water for pineapple and diversified agriculture crops, said Dole Hawaii Vice President Brian Orlopp. And draining the lake would kill the 500 tons of game fish he's trying to save, said Division of Aquatic Resources Administrator Bill Devick.
Suggestion: Nutrients in the water could be reduced.
Local response: The city hasn't calculated what it would cost to upgrade the Wahiawa sewage treatment plant, said Earl Ng, acting chief of wastewater treatment and disposal. Neither has anyone done cost-estimates on building holding ponds for rainwater runoff before it goes into the lake.
The Army Corps of Engineers group heard state and city plans for the lake - to remove up to 3,000 cubic yards, or 300 dump trucks-full per day until at least 30 percent to 40 percent of the surface is clear.
Salvinia can reproduce from pieces of plant so rapidly, it can double in size in two to eight days.
DEAN SENSUI / DSENSUI@STARBULLETIN.COM
The excavator's specially designed bucket can lift out 1.5 to 2 cubic yards of plant material at a time. The machine lifted out a scoop full of salvinia about every minute.
"The guys from Australia (who have battled it) called this the world's worst weed," said John Barko, a Corps director of environmental sciences, as he looked out over acres of thick, vibrant green. "A single bud smaller than a pen-point will generate a new plant."
The state plan could work, they said, because it includes spraying with an Environmental Protection Agency-approved herbicide to kill more of the plant and using floating oil booms to keep cleared waters from those still infested.
At best, however, the mechanical and chemical fight is expected only to hold the salvinia at bay.
Introducing as few as 1,000 salvinia weevils could ultimately control the salvinia population on Lake Wilson, because they multiply so well, Grodowitz said.
But that's not an option until the Hawaii and U.S. agriculture departments do testing to make sure the weevil, which loves salvinia, wouldn't also eat native Hawaiian plants. That could take months to years.
Other places, on the mainland, India, Australia and New Guinea, have effectively used the weevil to control salvinia with no side effects, Grodowitz said.
Even as experts worked to save the lake, an incident at the Wahiawa Wastewater Treatment Plant increased the problem.
About 48,000 gallons of wastewater bypassed the ultraviolet disinfecting process yesterday because of a faulty sensor, said staff at the state Health Department's Clean Water Branch. The city, which operates the plant, didn't respond yesterday to a request for comment on the accident.
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Basic facts about the
Lake Wilson cleanup
>> Surface covered with salvinia: 95 percent
>> Estimated volume of salvinia: 50,000 dump trucks
>> Cost to clear lake: Unknown, but could be millions of dollars
>> How long it will take: At least 100 working days, using three sites
>> Salvinia reproduces: From pieces of the plant as small as the head of a pin and also by spores
>> Estimated amount of fish in the lake: 500 tons
