Hungry fish have a job to do at Lake Fenwick

Grass carp to annihilate pesky weed

The carp are coming to the rescue at Lake Fenwick Park.

Kent city officials plan to stock Lake Fenwick this summer with as many as 600 grass carp in an effort to control Brazilian elodea, a noxious weed that threatens to overtake the lake.

“Our goal is to get the fish in there within a month and they eat like crazy and annihilate the Brazilian on the bottom,” said Matt Knox, a city environmental ecologist in charge of the project.

Over the last few years at Lake Fenwick, swimmers have become entangled in the aggressive weed. The weed also forms dense beds that reduce water quality. And the invasive weed could spread to other lakes if a small piece gets stuck on a boat that later enters a different lake, Knox said.

City officials have applied for a stocking permit from the Washington Department of Fish and Wildlife to do the task. It’s up to state officials to determine how many of the hungry carp can be stocked in the lake.

The lake is the highlight of the 140-acre park that lies just south of Reith Road at the base of Kent’s West Hill. The lake is fairly shallow and reaches 28 feet at its deepest point.

City officials tested the lake in 2000 and found the Brazilian elodea growing on the bottom. The weed had started to crowd out native plants.

“It’s kind of like blackberry bushes that take over your yard,” Knox said.

Brazilian elodea used to be a common decorative plant for home aquariums in the 1980s and 1990s. Due to its ability to infest lakes and other water bodies, Washington has since banned sales of the plant.

In the case of Lake Fenwick, it was most likely an aquarium that started the trouble.

“Someone probably dumped goldfish from an aquarium in the lake and that’s how it got established,” Knox said.

Grass carp are the only fish that eat the weed, and actually prefer it over other plants. Other jurisdictions also have used carp to control the weed. Knox said the city decided to try putting fish in the lake, rather than using an herbicide or bottom-barrier materials to keep the weed at bay.

“There are a number of lakes in Western Washington and throughout the United States where they have worked,” Knox said of the carp.

City officials also must install a fish screen at the lake’s outlet channel, to ensure the carp stay in the lake. A 40-foot culvert with angled sides and a few blocking bars will be used as a barrier.

The carp, which are sterile, will be about 8 to 12 inches long initially, but can grow as long as 4 feet and weigh as much as 40 pounds. Carp can grow as much as 10 pounds per year.

“The smaller (carp) start eating like crazy,” Knox said. “But they slow down as they get older.”

City officials have yet to figure out where they will purchase the special fish. Carp can cost anywhere from $5 to $15 each, according to the state Department of Fish and Wildlife. The city has received grant funding from the state to help pay for the project.

The fish would be transported to the Kent lake via tanker truck or possibly air-freighted in, Knox said.

Don’t expect to see dramatic results right away.

“Typically, it will take a couple of years before we notice much difference,” Knox said about how fast the carp might eradicate the weeds. “We’ll watch it each year and maybe have to add fish.”

Knox emphasized to anglers the importance of leaving the grass carp in the lake, although there are still opportunities to catch bass and rainbow trout at the lake.

“We encourage fishermen to leave these guys alone,” Knox said. “We hope to improve the fishing habitat in the long run.”

Knox didn’t know how many people might be willing to even eat carp.

“Somebody will eat anything anywhere,” Knox said. “But I don’t know of anyplace that serves carp burgers around here.”

Contact Steve Hunter at 253-872-6600, ext. 5052 or shunter@reporternewspapers.com.