STEVE INSKEEP, HOST:
The United States government is fighting an invasion.
DAVID GREENE, HOST:
The enemy is a fish - Asian carp.
INSKEEP: The U.S. Army Corps of Engineers is now permanently closed off northern parts of the Mississippi River to that invasive species.
GREENE: But that means they have also had to close it off to shipping. Here's Minnesota Public Radio's Matt Sepic.
MATT SEPIC, BYLINE: It's late on a Tuesday morning. And as it's done every day for decades, the Patrick Gannaway towboat pushes its two barges up the Mississippi River right through downtown Minneapolis.
(SOUNDBITE OF BOAT HORN)
SEPIC: To get its 2,400 tons of sand, gravel and limestone past the river's only waterfall, the barges take a five-story vertical ride inside the Upper St. Anthony Falls lock. Deckhands squeeze everything into the narrow chamber and use a winch to pick up the slack in the boat's steel cables. In a control room above, a lock operator closes the chamber's enormous gates before opening a valve and letting in 10 million gallons of rushing water. The towboat and its fully-loaded barges rise quickly - 49 feet in just 10 minutes. Doors at the other end of the chamber open and the Patrick Gannaway continues its journey upriver to a concrete plant.
(SOUNDBITE OF BOAT HORN)
SEPIC: But that was the boat's final trip through Minneapolis. Last year, Congress heeded scientists' warnings and ordered the lock closed to try keep invasive Asian carp from migrating further up river. Christine Goepfert with the National Parks Conservation Association says the carp - which can leap into boats - pose a big threat to the food supplies of other fish.
CHRISTINE GOEPFERT: They have disastrous consequences. They out-compete our native fish populations like our prized walleye. They basically vacuum up everything in their path. So now we know that the waters north of that lock will be protected from that threat.
SEPIC: Goepfert concedes that invasive carp may still migrate upriver. The fish could bypass the lock entirely if a careless boater neglects to drain ballast water or empties leftover fishing bait in an unaffected body of water. One thing that is certain, though, is that the lock's closure means the end of river shipping through Minneapolis. Randy Gaworski of Aggregate Industries, which owns the Patrick Gannaway, says it'll now be much harder to get construction materials to market.
RANDY GAWORSKI: I think anybody in the transportation business understands that the most efficient way to move material is via barge.
SEPIC: Gaworski says each barge trip hauls the equivalent of 110 semis; trucks that he says are now driving on already congested freeways. The lock opened in 1963 after a century-long civic effort to make Minneapolis the starting point for Mississippi River navigation. But historian John Anfinson says by that time, the flour milling industry that built the city was long gone and the lock never got the expected traffic. While Asian carp may have triggered the end of shipping here, he says it's been a long time coming.
JOHN ANFINSON: That lock and dam would not have closed had Minneapolis thought the lock was significant to its economy.
SEPIC: With commercial barges gone, city planners now hope to revitalize the down-at-the-heels industrial riverfront north of St. Anthony falls, replacing an old barge terminal with housing, businesses and a park. Anfinson says the end of navigation presents a once-in-a-century opportunity to rethink this city's relationship with the river. It's a conversation that's opening now that the gates of the lock have finally closed. For NPR News, I'm Matt Sepic in Minneapolis.
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