ST. PAUL, Minn. (AP) — Wildlife officials have captured hundreds of invasive carp from the Mississippi River near Trempealeau, Wisconsin.

The Minnesota Department of Natural Resources announced Dec. 1 that officials caught 296 silver carp, 23 grass carp and four bighead carp Nov. 30 in what the agency called the largest single capture of invasive carp in Minnesota to date.

Agency officials said the Wisconsin Department of Natural Resources tracked six tagged invasive carp in that area of the river the week that led officials to larger schools moving upstream. Observations from commercial anglers also helped officials pinpoint the fish.

The carp were imported to the U.S. in the 1960s and 1970s to help rid southern aquaculture farms of algae, weeds and parasites. They escaped through flooding and accidental releases, found their way into the Mississippi River and have used it as a superhighway to spread north into rivers and streams in the nation’s midsection.

Carp are voracious eaters — adult bigheads and silvers can consume up to 40% of their body weight in a day — and easily out-compete native species, wreaking havoc on aquatic ecosystems. There is no hard estimates of invasive carp populations in the U.S., but they are believed to number in the millions.

Wildlife officials are battling to keep them out of the Great Lakes and protect the region’s $7 billion fishing industry.

Grace Loppnow, the Minnesota DNR’s invasive carp coordinator, said the large number captured Nov. 30 is concerning but it’s likely they moved upstream and didn’t hatch in Minnesota waters.