A silver carp, a dreaded invasive fish known to knock people out of their boats, was found dead at the base of the Mississippi River dam at Winona, Minn., the farthest north the species has ever been detected and a clear sign that it can use its renowned jumping prowess to leap over barriers as it moves up from Iowa.

A worker with the U.S. Fish and Wildlife Service discovered the 30-inch-long carcass Aug. 9 atop a concrete abutment just below Lock and Dam 5, about 20 miles farther upstream from where the first — and only other — silver carp was found in the state, according to the Minnesota Department of Natural Resources (DNR).

The discovery has heightened concerns that the fish, the most alarming of four types of invasive carp that have infested rivers from Mississippi to Iowa and are threatening the Great Lakes, may be increasing in number in Minnesota.

“Finding this carp on the sill of the dam suggests that it was attempting to jump over it,” said Nick Frohnauer, the DNR’s invasive fish coordinator. “There’s no reproducing population here [yet], but that doesn’t mean we have a lot of time.”

Paul Labovitz, National Park Service superintendent of the 72-mile Mississippi National River and Recreation Area, was equally alarmed. The scientific community “is saying consistently that they are here. They are just not jumping into boats,” he said, referring to the fish’s tendency to leap out of the water when are disturbed by noises such as motors.

If they do become established, “that’s essentially the end of sport fishing and recreational boating” in Minnesota, he said.

In other states, Asian carp have become dominant species in rivers, displacing most other game and nongame fish. They are capable of eating 5 to 20 percent of their body weight each day by feeding on algae and other microscopic organisms, often outcompeting other fish for food. Scientists believe the fish could severely disrupt the aquatic ecosystems of Minnesota waters.

Of the four species, silver carp are believed to spread the most quickly, said Irene Jones, program coordinator for Friends of the Mississippi River. “And they injure boaters,” she said.

In the past several years a handful of bighead carp, another invasive species, have been found in Lake Pepin and the Mississippi and St. Croix rivers, and as far north as the mouth of the St. Croix in Prescott, Wis. But there is no indication they are established or reproducing, wildlife officials said.

The DNR and other agencies are working on a variety of strategies to stop the carp’s spread into Minnesota. They include installation of a $12 million noise barrier at the Ford Dam, which is supposed to improve its ability to block the fish but is not guaranteed to work. The Minnesota Legislature already has provided $7.5 million from the state’s 2008 Legacy Amendment for research and planning for a barrier, and has funded a $16 million upgrade to the Coon Rapids Dam that would also be a barrier — but which also would not be foolproof.

The most effective strategy would be to close the Upper St. Anthony Falls lock in Minneapolis, one of two dams on the river believed to be high enough to block their spread. The other is in Iowa.

That would protect the Mississippi watershed and the northern lakes that drain into it, but not the St. Croix and Minnesota rivers.

Earlier this year the Senate passed legislation authored by U.S. Sens. Amy Klobuchar and Al Franken to close the lock and dam at St. Anthony Falls within a year of its passage. The same bill was introduced in the House by U.S. Rep. Keith Ellison of Minneapolis, but is still awaiting action there.

Labovitz said the Park Service has been using an educational campaign to discourage recreational boaters from using the locks on the Mississippi. The hope, he said, is to reduce demand for the locks’ operations to the point that they will no longer be needed.

Asian carp were imported to the United States in the 1970s to clean fish ponds in the South. During floods, they escaped into the wild and have been migrating north along the Mississippi and its tributaries ever since. They have advanced to within 55 miles of Lake Michigan in the Illinois River, which connects with a shipping canal and other waters that reach Lake Michigan.

The Great Lakes region has been sharply divided over how to deal with the threat. Michigan went to court in an unsuccessful effort to force the closing of Chicago-area shipping locks, then joined four other states — Wisconsin, Minnesota, Ohio and Pennsylvania — in a lawsuit against the U.S. Army Corps of Engineers and Chicago’s water district, claiming their refusal to physically separate the watersheds was creating a public nuisance. A federal judge tossed out the case in December.

Debate on whether to close the shipping canal continues.