'We've seen fish gasping for air' at Lake Wilson
By Jan TenBruggencate
Advertiser Science Writer
Lake Wilson, the state's largest body of fresh water, is now so coated with the invasive salvinia weed that it is choking fish, clogging outboard motors and leaving anglers no open water into which to cast their lures.
Deborah Booker • The Honolulu Advertiser
It's even caused one bass fishing company to shut down.
State and county crews are trying to control the fast-growing salvinia weeds in Lake Wilson, which are hurting fish.
"It pretty much put us out of business," said Jeff Miller, co-owner with his wife of Hawai'i Bass Fishing, which took visitors on bass fishing trips by boat on the Central O'ahu reservoir.
The floating weeds are also harming fish.
"It's pretty thick stuff, and it seems to be cutting off oxygen for the fish," Miller said. "We've seen fish gasping for air near the surface. Not something you want to show to tourists."
State and county crews have been trying to control the fast-growing weed, but so far it has outgrown the equipment and herbicides being used against it, said Bill Devick, administrator of the state's Division of Aquatic Resources.
"Our biggest concern at this point would be if it were so abundant that there would be oxygen depletion due to decay," Devick said.
Rotting vegetation like dying salvinia can suck oxygen out of the water. And by coating the water's surface, the salvinia can block the entrance of new oxygen from the air into the water, he said.
"If this isn't controlled by summer, it could be a very serious problem," Devick said.
Low oxygen levels when the water warms up and lake levels are lower could result in a massive fish kill. There is an estimated 500 tons of fish in the 300-acre man-made lake. Lake Wilson is the largest freshwater body in the state by volume. Kaua'i's Waita Reservoir in Koloa has a larger surface area, but is shallower.
Salvinia molesta, the species in Lake Wilson, is a popular aquarium plant, but it is so invasive that its sale has been banned in many states, including California. Its sale is not prohibited in Hawai'i. It may have entered both Lake Wilson and Enchanted Lake by someone dumping unwanted aquarium contents into them.
"It's a little too late now, but I think it's idiotic to allow anyone to bring this stuff into the state," Devick said.
The City and County of Honolulu has been helping with equipment to clear the lake, but work with a backhoe has not been keeping pace with the growth, Devick said. The city plans to position a large excavator at the site, and hopes it will be able to do a better job, he said.
Government crews are also using a herbicide, Rodeo, to spray weeds in specific limited locations. Rodeo includes glyphosate, the same active ingredient as what's in the herbicide Roundup.
Rodeo is formulated for aquatic use and is not considered toxic to humans or animals at the levels being applied, Devick said.
The city is involved in the cleanup because it discharges treated sewage into the lake, and the nutrients associated with the sewage are helping make the salvinia grow faster.
Salvinia is listed by the federal government as a noxious weed and is on the state Division of Forestry and Wildlife's list of most invasive horticultural plants.
For fishing tour leader Jeff Miller, the weed has killed his hope for a profitable business. After a couple of years of work, the bass fishing tour operation was on the verge of being profitable when it was forced to shut down.
"We were just getting to the point of being break-even," he said. There is no other good bass fishing spot to which he can move the business, he said.
Internet surfers who visit his Web site, www.hawaiibassfishing.com, get this message: "Lake Wilson Alert. Due to the illegal introduction of salvinia into Lake Wilson, we are discontinuing our service until further notice."
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808)245-3074.
