This spring, an invasive silver carp bolted up the Mississippi River — right to the edge of where a researcher says the state has a chance to block the species from advancing any further.
The fish, tagged by the Minnesota Department of Natural Resources, took advantage of high water in May to slip around locks and dams as the river swelled and spillways opened.
A DNR report released to environmental groups this week showed the fish traveled about 35 miles against the current, from La Crosse, Wis., to just north of Winona, in less than a day.
It's the furthest north a tagged silver carp has trekked in the Mississippi, though some of the fish and other invasive carp species have been caught upstream, said Grace Loppnow, an invasive fish consultant at the DNR.
The progress of this carp's journey means it's time to block them at Lock and Dam 5, just northwest of Winona, said Peter Sorensen, a professor at the University of Minnesota who has made a career of studying carp. Sorensen's own data showed the invasive carp in the actual pool of that lock, with only a gate preventing further movement.
"It's the day of reckoning, in a way," he said.
According to Sorensen's research, this lock is the most likely place where a fish deterrent would work, because there isn't a large spillway that carp could use to swim around the structure. Sorensen and a group of engineers have developed one idea that might work there — a wall of bubbles and noise known as a "bioacoustic fish fence" that would span the lock pool and make the carp retreat.
But the DNR hasn't updated its plan for carp in years and hasn't evaluated Sorensen's plan.
Loppnow said that the agency needs time to convene the people with an interest in the carp problem, and that it needs to evaluate a range of solutions, not just Sorensen's idea.
The Stop Carp Coalition asked the DNR to start updating its plan for the invasive fish back in 2020, the same year that 51 silver and grass carp were pulled from waters near La Crosse.
Christine Goepfert, a co-chair of the coalition and associate director with the National Parks Conservation Association, said the advance of the tagged silver carp should inspire the state to act.
"This is like sounding the alarm," she said. "It's time to move forward."
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Silver carp are one of four invasive carp species that have been found in the Mississippi River and its tributaries. All of these fish can wreck the river ecosystem. Silver carp are excellent jumpers, able to launch up to 9 feet out of the water, Sorensen said.
The fish grow to 40 pounds and have been known to injure boaters on the water.
"If they hit you 6 feet out of the water, flat in your jaw, they break your jaw," Sorensen said.
The advance of these and other invasive carp are such a threat to the river that they were the main reason to permanently close the Upper St. Anthony boat lock in Minneapolis in 2015.
Goepfert said that was an effective block for the upper river, but said there's no real protection now for the waters downstream. That includes not just the Mississippi but Lake Pepin, the St. Croix River and the Minnesota River.
Time is of the essence for another reason, according to Colleen O'Connor Toberman, land use and planning program director for Friends of the Mississippi River.
If the DNR is able to move quickly and identify next steps, the agency could ask for funding for a barrier at Lock and Dam 5 this autumn and potentially get it in the state budget, she said. But if that deadline is missed, Minnesota's biennial budget means there won't be another opportunity for two years.
Right now, an engineering report Sorensen provided on his proposal pegs the cost at between $8.25 million and $16.5 million.
According to the DNR's report on the rogue carp, there isn't any evidence that the fish has reproduced in Minnesota waters. But that doesn't mean it isn't happening, Sorensen said — carp eggs are tiny and hard to find in the long stretches of river between each dam.
Loppnow said that the DNR will move some of its larval sampling up the river to the area where the tagged carp was tracked, and start trying to catch fish there as well.
"We need to get out there and do some sampling, and unfortunately with the high water, it's unsafe to go out there and net right now," Loppnow said.
