TRAVERSE CITY, Mich. — Genetic material from an invasive fish called the Eurasian ruffe has been found in southern Lake Michigan for the first time, raising the possibility that it could migrate into the Mississippi River watershed and compete with native fish there, a scientist said Tuesday.

Researchers testing Great Lakes waters for signs of Asian carp and other invasive species detected DNA from the ruffe in two samples taken in July from Lake Michigan’s Calumet Harbor at Chicago, said Lindsay Chadderton of The Nature Conservancy, a member of the team.

No actual ruffe were seen. State and federal officials downplayed the likelihood that the DNA discovery signaled a significant presence of the exotic fish even as they urged anglers to be on the lookout for them. Still, Chadderton urged the agencies to take the threat seriously and step up monitoring of Chicago-area waters.

“This could be the first indication that Eurasian ruffe are on the cusp of using the Chicago canal system to invade the Mississippi,” he said.

An engineered network of rivers and canals in and around Chicago is the flashpoint in a regional debate over invasive species. Five states have urged federal courts to order measures that would sever links between the Great Lakes and Mississippi systems, preventing fish and other organisms from moving between them.

The U.S. Army Corps of Engineers, under orders from Congress, has pledged to produce a list of options by early next year, including placement of barriers in the waterways.

The Eurasian ruffe is among 29 species the Corps has identified as leading candidates to migrate between the two systems. A small fish that resembles and is related to the yellow perch, it is believed to have hitched a ride in a freighter’s ballast tanks from Europe to Lake Superior’s Duluth Harbor in the mid-1980s.

It has spread across Lake Superior and to limited sections of northern Lake Michigan and Lake Huron, where it competes for food with perch and walleye, two prized sport and commercial species. Even so, the U.S. Fish and Wildlife Service says native species don’t appear to have been significantly harmed.

The Nature Conservancy, the University of Notre Dame and Central Michigan University have been sampling Great Lakes tributaries and bays since 2009 for genetic fingerprints of invasive fish. They’ve found Asian carp DNA in the Chicago waters and in Lake Erie.

Fish leave their DNA in slime and body wastes. Army Corps scientists say it also can be transported by birds, boat hulls and fishing nets.

Kevin Irons, aquatic nuisance species program manager for the Illinois Department of Natural Resources, said it’s not surprising that Eurasian ruffe DNA would turn up in Calumet Harbor, with its heavy commercial shipping traffic. State agencies monitor the harbor with electrofishing and nearshore waters of Lake Michigan with nets.

“To date, we have not captured any ruffe, and in fact we don’t believe Eurasian ruffe are established anywhere in southern Lake Michigan,” Irons said.