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With a historic $17 billion state budget surplus this year, environmental advocates hoped Minnesota lawmakers would make a big investment to stop the advance of invasive carp up the Mississippi River.

“It was an opportune moment to do some big things this year,” said Whitney Clark, executive director of the nonprofit Friends of the Mississippi River, a member of the Stop Carp Coalition.

The coalition urged lawmakers to approve about 

 for prevention measures, including installing a bio-acoustic fish fence at Lock and Dam 5 near Winona. The system uses bubbles, sound and light to deter invasive carp from swimming upstream. It’s currently being tested on the Cumberland River in Kentucky.

Instead, Minnesota lawmakers included a fraction of that amount, $1.72 million, in the omnibus environmental 

 to expand the Minnesota Department of Natural Resources’ invasive carp prevention and management efforts. Clark said they missed a key opportunity.

“I think people will be very, very shocked and disappointed if something that was preventable was allowed to happen because of inaction or decisiveness, at a moment when we still had an opportunity,” he said.

Silver carp are one of four species collectively known as invasive carp, along with grass, black and bighead carp. They’ve been moving up the Mississippi River and other waterways since they were accidentally released into Arkansas waters in the 1970s.

Invasive carp are fast-growing and voracious eaters, outcompeting native fish for food and leading to a decline in biodiversity and water quality in rivers where they're established.

Silver carp are known to jump out of the water, sometimes injuring boaters. That’s made for popular 

. But they also present a serious environmental challenge.

University of Minnesota Professor Peter Sorensen has been studying invasive carp for a decade, including their behavior, movements, impacts and how to stop them from moving upstream and reproducing.

“It's not one adult silver carp that really is a big concern,” he said. “It's when they have babies, and you're looking at hundreds of thousands of young. Then you have a really serious problem.”

Individual invasive carp have been caught as far upstream as the Twin Cities metro. In 2020, 51 carp were 

 just south of La Crosse, Wis., downstream from Winona.

This year on March 20, the day a Senate committee held a hearing on the barrier funding bill, the DNR announced commercial anglers had 

 near Winona, the largest single catch of invasive carp so far upstream. 

Sorensen’s lab has been testing the bio-acoustic fish fence, or BAFF, with promising results.

Invasive carp have exceptionally sensitive hearing, especially to higher frequencies. The BAFF projects sound onto a stream of air bubbles, creating a wall of sound that invasive carp avoid.

Sorensen said Lock and Dam 5 is an ideal location to keep invasive carp out of the upper Mississippi, for several reasons. There are no side channels or bypasses around the dam, and its spillway gates are only open a fraction of the year. 

Also, there’s a relatively small pool of water above the lock and dam, trapping any invasive carp that get through.

Sorensen thinks a barrier should be one of several strategies to combat invasive carp at Lock and Dam 5, along with adjusting spillway gates and physically removing carp above and below the dam.

The BAFF system is not a silver bullet, he said, but could be a reasonable stop-gap measure that would last for the next couple of decades.

“If they do get through and they spawn, I know of no technology approach that can even come close to controlling hundreds of thousands of fish above that location,” Sorensen said.

Minnesota DNR officials say more work is needed to determine whether the bio-acoustic fish fence is the best solution. 

Before spending millions of dollars, the agency said it wants to evaluate all the available technologies and possible locations through a strategic decision-making process with help from the U.S. Geological Survey.

That process is currently underway and on track to wrap up by December, said Heidi Wolf, who heads the DNR's ecosystem management and protection section. 

“It's to get the right people in the room, including stakeholders and citizens of Minnesota, to say what are our values? What are we looking for here? What makes sense for Minnesota?” she said. 

Wolf said the BAFF’s engineering design was only about 10 percent complete. And there were lingering questions, including who would own and operate it and what it would cost to maintain.

There are other promising designs that could be less expensive, Wolf said, including an acoustic deterrent system that the U.S. Army Corps of Engineers is testing at Lock and Dam 19 on the Mississippi River in Keokuk, Iowa. 

The DNR is still formulating a plan for how to spend the $1.72 million appropriated by the Legislature, Wolf said. The bill designated $325,000 for the University of Minnesota to study changes in dam spillway gates that could help prevent invasive carp from getting through.

The DNR also might increase its commercial fishing efforts that target invasive carp, Wolf said, as well as tagging and tracking the fish to learn more about their movements.

And the agency wants to learn more about the potential impacts of a barrier on native fish traveling upstream.

Advocates worry that further delaying the installation of a barrier could put the river at risk. 

If invasive carp become established in Minnesota, they'll have devastating impacts not only on the river's ecosystem, but also the economy, tourism and recreation, said Colleen O'Connor Toberman is Friends of the Mississippi's land use and planning director. 

“If a silver carp can jump 10 feet in the air and knock you out of your boat and give you a black eye, give you a concussion while you're trying to go out fishing or hunting or waterskiing, that is a unique impairment, and people won't go on the water,” she said.

Sorensen said he’s also concerned about a barrier’s impacts on native fish, but thinks they could be lessened by installing a 

 which has been used in other rivers to carry migrating fish over a dam.

In some rivers where invasive carp have established themselves, the native fish population has plummeted by 50 percent, he said.

“So lack of action in itself will be disastrous to native fish on a permanent basis,” he said.

The DNR said there's no evidence that invasive carp are reproducing in Minnesota waters yet.

But advocates say without a major investment to stop them, it's only a matter of time before they're here to stay.

“We either invest now, or we pay later,” O’Connor Toberman said. “There is no way to avoid the expense of invasive carp.”

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The Department of Natural Resources says more work is needed to determine the best option to prevent the invasive fish from moving upstream into Minnesota waters. But environmental advocates worry time is running out.

Funding for invasive carp barrier in Mississippi River falls short at Legislature

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