A proposal to install a carp deterrent system on a lock and dam near Winona, Minnesota has received funding from the state of Minnesota’s Outdoor Heritage Fund. Once installed, it should help protect both the upper Mississippi and the St. Croix Rivers. The proposal to use several different methods at the key point has been discussed for years, with scientists saying it could prevent widespread infestation of waters upstream.

The new deterrent system will seek to drastically reduce the number of fish that make it up the Mississippi. Because the barrier will be located on the Mississippi between the reproducing carp populations and the mouth of the St. Croix, the system is expected to help protect the St. Croix.

“Without a carp deterrent, the native fish and river ecosystem did not have a chance; now they most definitely do,” said Dr. Peter Sorensen, Professor Emeritus, University of Minnesota. “No other state has taken significant action before it was too late. Minnesotans should be proud.”

While numerous invasive carp have been found in the St. Croix already, biologists believe the fish are not yet reproducing in these waters. The fish that have been found are thought to have traveled up the river from parts of the Mississippi near Iowa and Illinois where the invasive species are abundant. In March 2020, authorities reported that 40 adult invasive carp had been captured in Pool 8 of the Mississippi, the first population believed to be breeding in Minnesota and Wisconsin waters.

The bill, which is expected to be signed by Governor Tim Walz soon, will provide $12 million from Minnesota’s Outdoor Heritage Fund. The money will let the Department of Natural Resources work with federal agencies to install a sound and bubble barrier at the lock and dam, a method that is believed to prevent most carp from passing.

Funding that was considered last year was removed at the last minute, opening a rift between advocates and the Department of Natural Resources over the strategy. The DNR was again critical of the proposal this year, but its objections went unheeded. The agency believes the benefits of such a barrier are possibly overstated. Officials say they believe it’s the best option available.

“There is no other strategy except ‘let the carp come,’” said David Hartwell, chair of the Lessard-Sams Outdoor Heritage Council.

The project is based on a 2020 report by Sorensen, which he completed at the request of the legislature. Sorensen has led numerous laboratory and field studies of carp behavior, biology, and deterrents. This research has revealed that carp are especially susceptible to sound combined with other stimulus. Sorensen believes a sound-and-bubble barrier could block up to 99 percent of carp from passing upstream.

“In contrast to simple sound fields projected by speakers on their own, a bio-acoustic fish fence system (BAFF), which couple sound with a bubble curtain and strobe lights, seem to have promise,” Sorensen wrote. “To date, commercially-available BAFF systems have shown remarkable promise in half a dozen lab and field studies.”

Invasive carp were first brought to the United States from China in 1963. Imported to Arkansas for use in sewage ponds and aquaculture farms, the fish escaped into the Mississippi River system and have been slowly working their way north ever since. Invasive carp pose several threats to the St. Croix River, including being voracious eaters and prolific breeders, allowing them to quickly dominate the ecosystem. This has led to drastic declines of native fish populations in other areas.

In addition, one species, silver carp, are known for leaping out of the water at the sound of passing boats. The fish can weigh anywhere from 20 to 80 pounds, and do serious damage to people and property. Environmental groups have long urged governments to do more to prevent carp from infesting the upper Mississippi system while it’s still possible.

“It’s been over 10 years since we sounded the alarm on the threat invasive carp pose to our prized waterways and fisheries,” said Christine Goepfert, Midwest Campaign Director for the National Parks Conservation Association and co-Chair of the Stop Carp Coalition. “We now have new tools to fight these invaders, and we’re thrilled to see the state step up with funding to help keep them out. A physical deterrent is just one of many in our multi-pronged approach for stopping carp from invading waters that flow through our nearby national parks, including the Mississippi National River and Recreation Area and the St. Croix National Scenic Riverway.”

In addition to the acoustic bubble barrier, the strategy to prevent the spread of carp includes continued monitoring of the population and ongoing efforts to manually remove any fish from the upper river that make it through the lock and dam.

The funding legislation requires design of the barrier system to be completed in two years, and fully installed within five years.