The Wisconsin Department of Natural Resources said a bighead carp was caught in the Lower Wisconsin River near Lone Rock while "environmental" DNA sampling on the St. Croix River in the northwestern of the state has turned up positive samples of silver carp, the Milwaukee Journal Sentinel reported Thursday.
The silver and bighead species of Asian carp worry biologists because of impacts they can have on native ecosystems.
Imported into North America by Southern fish farmers, the carp have been migrating north for decades after escaping their containment ponds.
Most of the efforts against the carp so far have been directed at protecting the Great Lakes, officials said, but inland waterways are an area of major concern.
"We need the federal government to recognize the importance of the Mississippi River basin's invasive species problem and give it the attention and funding it deserves," Bob Wakeman, the DNR's invasive species coordinator, said.
Asian carp were first detected in the Mississippi River along Wisconsin's western border 15 years ago but this is the first time a bighead carp has been found in the Wisconsin River, the DNR said.