Fear of a fish will bring an end to continuous navigation on a portion of America's greatest river.

In an effort to prevent the advance of invasive carp, Congress appears poised to close the Mississippi River shipping lock at Upper St. Anthony Falls in Minneapolis within a year, Minnesota's congressional delegation said Tuesday.

The closure, which could happen as soon as Memorial Day, won't be a done deal until the House and Senate approve a larger water infrastructure bill and President Barack Obama signs it.

The closure, once seen as a long shot, now appears likely after bipartisan members of a conference committee agreed on the proposal.

The carp -- silver and bighead carp often called Asian carp -- are voracious feeders of plankton and can imperil native fish by undercutting an entire ecosystem. A shipping lock can allow the fish to reach waters above a dam, so closing the lock is seen as one of the most effective barriers to halt the carp's march upstream.

The fish has yet to establish itself in Mississippi River waters in Minnesota, but it has been advancing, and carp eggs were found this winter below Lock and Dam No. 8 in Genoa, Wis.

Many biologists say that once established, the carp is nearly impossible to eradicate.

The two locks at Upper and Lower St. Anthony Falls are the least used of the 29-lock system between the Twin Cities and Granite City, Ill., and the bipartisan agreement drew praise..

"It shows you what leadership can do when they get focused on meaningful action," said Whitney Clark, executive director of Friends of the Mississippi.

But it's not without costs.

The locks, which were completed in 1963, are used by a handful of companies to haul barge loads of material upriver, including tons of rock used to make concrete for the new Vikings stadium and many construction projects across downtown Minneapolis.

Eagan-based Aggregate Industries regularly ships barges carrying some 1,200 tons of material from its hub near St. Paul's Homan Field to its yard in northeast Minneapolis. Its largest customer is Cemstone, whose concrete mixers are a construction-site fixture.

"Concrete is a perishable product," said Tim Becken, a senior vice president at Cemstone. "Typically, you only haul this product for 25 minutes to a half hour, so you need to make it close to where you're going to pour it. It's the Vikings stadium ... it's apartments, it's buildings, you name it."

Aggregate says the only viable shipping alternative is by truck -- an estimated 20,000 additional one-way truckloads annually, the company says.

"And it's quite a bit more expensive than using barges," said Becken, who didn't have specific estimates.

He said he doesn't oppose closing the locks, but he said the companies will lobby to be compensated and increased heavy truck traffic is likely.

Within the past two years, a number of lock-users have reduced or eliminated their lock use to lower the chances of carp swimming through. Several entertainment cruise boats have relocated below the falls, and recreational boaters have reduced their use. More than a year ago, the National Park Service, Wilderness Inquiry and Friends of the Mississippi stopped taking flotillas of canoes through the locks as part of popular river tours.

The congressional action was spearheaded by Sen. Amy Klobuchar, who attended "carp summits" convened by Gov. Mark Dayton.

"The spread of invasive carp poses a major threat not only to Minnesota's environment, but also (to) the recreation and fishing industries that help power our state's economy and create jobs," Klobuchar said in a statement.

Closing the locks, scientists say, should protect waters upstream, although the move will not be the only protection.

The Coon Rapids Dam is being renovated this year to make it a more effective barrier, though fish still could get past the structure during severe floods. Above Coon Rapids lies the Rum River, the outlet of Lake Mille Lacs, one of the state's most important fishing lakes.

Dams farther upstream likely would hinder the fish's advance through the heart of Minnesota's fishing and boating waters toward the river's headwaters of Lake Itasca.

The locks' closing is expected to raise a question of what will become of more than $10 million the Minnesota Department of Natural Resources plans to spend on an electrical, light and sound barrier below the Ford Dam in St. Paul, also known as Lock and Dam No. 1.

And farther downstream, University of Minnesota carp researcher Peter Sorensen has a $60,000 plan to install underwater speakers as a carp-deterrent below Lock and Dam No. 8.

Many experts say the key battles against the invaders must be fought in southeastern Minnesota before the fish can have access to the Minnesota River -- believed to be prime habitat for bighead and silver carp -- and the St. Croix River.

"Closing the lock is really helpful for all the waters above St. Anthony Falls," Clark said.

"But for all the waters below the falls, this does nothing. We still have a lot of work to do."