It's an ugly brute with a gaping mouth and eyes that hang low on its face. Someday soon, with two of its equally odious cousins, it could take over Minnesota's rivers and lakes, squeezing out native species. Unless somebody stops them.

That's why the arrival of a 27-pound bighead carp in the St. Croix River on Monday triggered alarm among Department of Natural Resources officials, who fear the invasive carp could damage Minnesota's aquatic ecosystems and threaten its treasured walleyes and sunnies.

Naturalists said that the lunker probably swam upstream from Iowa and that there's no sign the carp are reproducing in Minnesota.

Nonetheless, its arrival couldn't have occurred at a more politically opportune time. Gov. Mark Dayton has proposed $16 million in state bonding to rebuild the Coon Rapids dam as a barrier to stop the carp from spreading to Minnesota's prime fishing lakes north of the Twin Cities. State officials are also pressing federal authorities to close, at least temporarily, one of the lock and dams between Red Wing and Minneapolis to create a barrier farther downstream.

"This is not a crisis," said Luke Skinner, the DNR invasive species supervisor. Asian carp have been found in Minnesota seven times since 1996, most recently in January 2009. "But they are knocking on our door," he said.

National attention has focused on the Asian carp's imminent arrival in Lake Michigan and the Great Lakes via the Illinois River near Chicago.

But a press conference held on Wednesday in St. Paul reflected DNR officials' fears and frustrations. "Much of the focus is on Chicago and the Great Lakes," Skinner said. "We need to divert that attention to Minnesota."

The 34-inch bighead displayed in a trough of bloody ice at the DNR headquarters on Wednesday was certainly eye-catching enough.

It was caught Monday by a commercial fisherman in the St. Croix River near Prescott. DNR fish biologist Brad Parsons said it was a "flyer," a mature, healthy bighead that most likely swam up from Iowa on the high spring flow of the Mississippi. This time of the year, locks and dams are wide open to allow torrents of water to flow south.

Four invaders

The bighead is one of four species of Asian carp that are considered invasive to American rivers. It is not the dreaded leaping carp that can knock people out of their boats - that's the silver. But it can grow to 110 pounds and cause havoc for native fish.

Asian carp were imported from China in the 1970s to control plankton in aquaculture ponds. By the early 1980s, both the bighead and the silver carp had escaped into open waters in the South.

All of them can do massive ecological damage. Parsons said that bighead eat 40 percent of their body weight every day in plankton and bugs. "They really upset the food chain," he said, and replace other game fish in their ecosystems.

In the Missouri River, where carp are well established, they now make up 90 percent of the fish population, he said. Last week, a carp-removal project in Iowa pulled 43 tons of the invasive fish from a 17-mile stretch of the Mississippi in four days.

At this point the closest reproducing population is in Iowa, Skinner said.

The only thing that will stop them is a natural or man-made barrier. Taylor Falls east of the Twin Cities, for example, will likely stop their spread up the St. Croix, Skinner said. St. Anthony Falls would have stopped them at Minneapolis -- except for the lock and dam installed there decades ago to facilitate shipping.

In Chicago, an electric barrier was set up to prevent carp from reaching Lake Michigan through a shipping canal, and a lawsuit is pending on whether to close the canal for good.

Dams or locks

On the Mississippi, naturalists say there are two options. One is to close one of the locks, which would require federal approval. Skinner said discussions are underway, though the Army Corps of Engineers has said it would agree only under an act of Congress.

The other option, which is within the state's power, is to rebuild the Coon Rapids dam. That would essentially mean sacrificing the lower length of the Mississippi, including Lake Pepin, and the Minnesota River to carp invaders. But it could preserve the state's $4 billion fishing industry up north.

That, however, is controversial as well. It would require $16 million, and, according to some, it would work for only 10 or 15 years and might not be adequate at times of high water.

Paul Labovitz, superintendent of the 72-mile Mississippi National River and Recreation Area, says it would be more effective to simply close the locks at Lock and Dam No. 1, a massive structure below the Ford bridge, or the Upper St. Anthony Lock and Dam, a 49-foot drop near downtown Minneapolis' Stone Arch Bridge.

Whatever the state does, Skinner said, it has to happen fast.

"We need action," he said. "Soon."

Staff writer Paul Walsh contributed to this report.

Josephine Marcotty - 612-673-7394