Minnesota conservation officials said Thursday that a silver carp, the kind that in other states is known to leap out of the water and cause havoc for boaters, was found for the first time in the St. Croix River.
The discovery of the destructive carp in one of the region's most pristine rivers was "disappointing but not unexpected," DNR invasive fish coordinator Nick Frohnauer said in a statement.
He noted the fish was caught near Prescott, Wis., where the St. Croix empties into the Mississippi River and that "in 2014, two silver carp were found in the Mississippi only a short distance upstream from where the St. Croix and Mississippi meet."
The silver carp caught by a commercial angler on the St. Croix was 33 inches long and weighed 13 pounds.
One bighead carp was also caught by the commercial angler, who was working with a DNR fisheries biologist. Bighead carp have previously been caught at this same location and further upstream on the St. Croix, the DNR said.
Bighead, silver and other invasive carp have been making their way upstream since escaping into the Mississippi River in the 1970s. These large fish compete with native species and pose a threat to rivers and lakes.
While no breeding populations have been detected in Minnesota waters, individual fish have been caught in the Mississippi near the Twin Cities, the St. Croix River and the Minnesota River, where a a 25-pound male bighead carp was caught last year near New Ulm, Minn.
While the DNR is concerned about the potential impacts of invasive carp in the St. Croix, the individual fish that have been captured do not indicate reproduction or an established population of either bighead or silver carp in the St. Croix, Frohnauer noted.
"The location where the carp were captured is a well-known over-wintering area for several species of fish," he said. "At this time, it is hard to predict if these individuals would have moved further upstream the St. Croix River, or back into the Mississippi River when water temperatures warm up in the spring."
Once the ice clears, DNR staff plan to search for more carp near Prescott. They'll also sample at the King Power Plant near Bayport, Minn., where bighead carp have been caught in the past.
Officials pointed to defenses Minnesota has in place already to thwart the invasive creatures. Two years ago, the Upper St. Anthony Falls Lock and Dam in Minneapolis was closed to try and stop invasive carp from gaining access to the upper Mississippi River above the St. Anthony Falls.
University of Minnesota researchers along with the DNR have also been testing carp deterrents, installing acoustic speakers at Mississippi River dams at Hastings and in far southeastern Minnesota.