There's a one-word explanation for the dramatic downturn in waterfowl on the shallow 50,000-acre lake 30 miles south of Burns: carp.

BURNS — Biologist Linda Beck stands in water halfway to her knees, gazing out on a lake strangely empty of waterfowl. Cormorants, pelicans, gulls and terns by the millions once wheeled and shrieked above Malheur Lake while ducks bobbed and dove for insects. Now, the lake and sky are eerily empty.

"I mean, there are no birds," said the 35-year-old fish biologist for the U.S. Fish and Wildlife Service, splashing to dry ground on the north shore on a recent afternoon. "We still should be seeing some birds."

There's a one-word explanation for the dramatic downturn in waterfowl on the shallow 50,000-acre lake 30 miles south of Burns: carp.

Their ranks have exploded over the course of decades — and nothing, not even a succession of wholesale poisonings, has beaten them back for long.

Carp out-compete the waterfowl for Sago Pondweed, aquatic invertebrates, insects and other food. They also root on the lake bottom, stirring up sediment and diminishing the sunlight necessary for the growth of lake grasses. "It's a giant carp pond," said Bob Sallinger, spokesman for the Audubon Society of Portland. "That lake is basically a dead lake."

Migratory waterfowl, shore birds and colonial waterbirds used to darken the sky above Malheur Lake and the 187,000-acre refuge during their annual stop on the Pacific flyway. Duck production alone averaged more than 101,000 annually with a peak of 139,000 in 1946.

No more. Waterfowl production is down 75 percent at the refuge and visiting bird numbers have fallen by several million a year, according to the Fish and Wildlife Service.

The fish invaders have caused problems on the refuge since the 1940s. The federal agency has poisoned the lake and tributaries with an odorless chemical poison called rotenone multiple times in unsuccessful efforts to kill them off, the last time 1992.

But rotenone hasn't proven a long-term solution — the carp populations return in force within four years, Beck said.

Part of the difficulty is that carp inhabit the Silvies River and can restock Malheur Lake when the river and lake flow together during cyclical wet weather, about every seven years, she said. Another factor is that a 5-pound female carp can produce 500,000 eggs per year for 30 years.

The federal agency has a group of experts weighing other possibilities, including commercial harvesting, organic fertilizer, feed for livestock and fish, and alternative energy fuel. Two others are:

Consumption by Russian Orthodox Church believers, for whom carp is a traditional food.

U.S. anglers often regard carp as a "trash fish," complaining the meat is bony and oily, but "I had some that was smoked and I loved it," Beck said.

Removal of carp pituitary glands for injection into other fish species to accelerate sexual maturity and aid spawning. One gram of diluted carp pituitary can bring $350, Beck said.

Still, it may be years before the refuge can gain control over the carp. "There are some really tough issues to grapple with," said Sallinger, a working group member who suspects the battle against carp will guide refuge polices for 15 years.

Carp are native to Europe and Asia and were artificially introduced into the Silvies River in about 1920, probably to keep nearby irrigation canals open on the premise that carp would eat aquatic plants and algae, Beck said.

Their numbers in Malheur Lake — which averages 18 inches deep — verges on the unbelievable. Biologists estimate 1.5 million carp inhabit the lake, although nobody knows for sure. Collectively, they could weigh 7 million pounds.

An average carp is a rich golden color and weighs 5 pounds, while some tip the scales at 17 pounds and a few 80-pounders are possible, said Przeyslaw Bajer, a research associate studying carp at the University of Minnesota at St. Paul. They sometimes live 50 years, he said.

Some scientists believe carp are smarter than other fish species, said Bajer, a recent visitor to Malheur Lake and a member of the working group. "They have a good memory," he said. "I think they can remember at least the layout of the lake and where different things are."

They're also tough — tolerating water temperatures ranging from near-freezing to 86 degrees, Beck said. When water turns shallow, they sometimes burrow into the bottom, which allows water to flow in and giving them a deeper environment, she said.

One solution — fishing — isn't a possibility for now. The refuge doesn't allow the public to angle for carp in Malheur Lake. And winning approval would likely be an unwieldy process involving insertion of a proposal in the Federal Register in Washington, D.C., and probably would take two years, Beck said.

On windless summer days, when Malheur Lake's surface becomes still, Beck said she sometimes stands on the deck of one of the refuge's two shallow-draft airboats watching the dorsal fins of thousands of carp stir the water in circles an inch or two above the surface.

They remind her of the great white shark in "Jaws."

"You just kind of look out across the lake and you see the fins," she said. "It's crazy."