Something to carp about at Green Lake

Imagine a 40-pound carp tickling your toes next time you dip them into murky Green Lake, Seattle's unofficial public aquarium.

Goldfish, turtles, trout and even caiman have been dumped into the lake. Now the city wants to plant 800 to 1,000 voracious, grass-eating carp to devour the pesky Eurasian milfoil that turns the lake into an aquatic jungle each summer.

The Seattle Parks Department has been battling the noxious weed for years with limited success and has resorted to mowing the tops and selectively plucking them like aquatic dandelions near the swimming beaches.

Now it's the turn of the homely grass carp, native to the Amur River, which borders Russia and China. The fish, an overgrown minnow, is vegetarian and a near constant feeder. It has been planted in about 100 lakes and ponds across Washington state to combat aquatic weeds.

So many were added to Silver Lake in Cowlitz County they stripped it of all vegetation. Homeowners tell of hungry grass carp schooling along the shore when they mowed their lawns, slurping up stray clippings.

The city has turned to the state Department of Fish and Wildlife--the folks who planted 150 tiger muskies in Green Lake last month to eat undesirable fish such as perch and European carp, a bothersome cousin to the grass carp. The Fish and Wildlife department has developed a stocking plan for the grass carp.

The grass carp "will chow down on plant material, and in Green Lake it's 99 percent Eurasian milfoil," said Kevin Stoops, the Parks Department manager for major projects and planning.

There's one hitch. The grass carp--which by state law must be genetically sterilized before being dumped into the lake--apparently don't like eating milfoil, preferring more delectable water plants.

Stoops doesn't think that will be a problem. "Given that it's the only thing out there, they will eat it," he predicts. "Hunger is a strong motivator."

And will the newly planted tiger muskies eat the newly planted grass carp? Or might they eat baby grebes, ducklings and other waterfowl, as some lake-loving residents fear? Or swimmers?

Not according to state wildlife officials.

The tiger muskies and carp won't mess with humans, and the muskies probably won't eat the carp because the carp will be at least 10 inches long and they grow fast, Stoops said.

Tiger muskies, a bullet-like cross between the toothy northern pike and muskellunge, will devour other fish, like pesky perch, rock bass, pumpkinseed sunfish and baby European carp.

The European carp, unlike the grass carp, are undesirable as far as parks officials are concerned. Unlike the grass carp, which pick and pull at vegetation, the European carp root at the bottom of the lake like rototillers, stirring up the nutrient-rich muck. The nutrients then fuel algae blooms, another problem at Green Lake. The state had to temporarily close the lake last year when a blue-green algae bloom tested toxic.

In an effort to fight the algae, the city had 181 tons of alum and 76 tons of sodium aluminate spread across the lake in 1991. It temporarily stripped the lake of phosphorus, which had fed the algae, and cleared up the lake.

But it's a delicate balance. The new water clarity allowed more sunlight to penetrate the lake, and coupled with the rooting European carp, the milfoil grew just "hunky-dory," said Martin Muller, a board member of the Green Lake Park Alliance. While not speaking for the board, Muller questions whether it makes any sense to stock the lake with either tiger muskies or grass carp.

"The major concern is the Parks Department and state Fish and Wildlife are always fighting the symptoms in Green Lake but not the cause. You can never change one thing. Something else is going to happen," Muller said.

Green Lake would be better off if milfoil was hand-picked by scuba divers, as was proposed last year by volunteers. The project never happened, with volunteers blaming the city.

A more extreme measure would be to dredge Green Lake and remove its "biologically active" bottom layer, Muller said. Or the city could cap the lake bottom with clay, which would thwart milfoil. Those alternatives would be costly, but the city must attack the root cause of Green Lake's problem--the amount of nutrients in the water, Muller says.

Green Lake is more of a puddle than a lake. It averages only about a dozen feet deep. A 25-foot-deep channel extends along the lake's eastern shore and is more often clear of milfoil.

Landlocked, with no fresh source of water, the lake is stagnant, fed by rain and occasional overflows from filtered stormwater runoff. When repairs are made to the Roosevelt and Maple Leaf reservoirs once or twice a year, the city dumps between 50 million and 70 million gallons of fresh water into Green Lake.

"Other than rain, it's the only dilution we get anymore," said Margaret Anthony, Parks Department north division director.

Like many urban lakes, Green Lake has become a convenient dumping spot for unwanted pets, the most notorious of which were a pair of sickly caimans. The caimans, small cousins of the crocodile, were set free in 1986. After startling a few unsuspecting visitors, they were captured at the north end of the lake where they were found snoozing one night.

The goal for the lake is to keep its ecology and health in balance, said Anthony. As the most visited park in the city, "it's a gem for us, and we definitely want to take care of it."