CHICAGO, IL — Wildlife agencies are stepping up waterway testing efforts following a spike in invasive Asian carp DNA detections in the Chicago River about five miles from Lake Michigan.

On Friday, Nov. 1, state and federal officials announced plans for a two-week intensive sampling effort in the Chicago River’s south branch after routine fall testing yielded 76 hits of environmental DNA, or eDNA, for silver and bighead carp.

The hits came from Bubbly Creek, a nickname for the south fork of the river’s south branch located in the city of Chicago.

The “proximity and abundance” of eDNA hits – 49 for silver and 27 for bighead carp — “are much higher than values seen previously in this area,” according to a joint news release by the Illinois Department of Natural Resources and the U.S. Fish and Wildlife Service.

The wildlife service collected 414 samples between Oct. 8 and 10 in the Chicago Area Waterway System downstream of electronic barriers that are supposed to block the invasive fish from reaching Lake Michigan and spreading throughout the Great Lakes basin.

No live fish were found. No other waterways tested positive for carp DNA.

Invasive silver and bighead carp are seen as a major threat to the Great Lakes fishing industry because they outcompete native species for food and habitat. The fish are also considered a safety threat to boaters because they leap from the water when startled.

A study published this summer in the journal Freshwater Biology concluded the relatively low plankton supply in Lake Michigan would likely not impede a carp population from becoming established because the fish could thrive on a diet of feces and other detritus matter.

“This sampling and assessment effort, done out of an abundance of caution, will be similar to that which would be used if a live Asian carp had been captured,” said Kevin Irons, manager of the Illinois DNR aquatic nuisance species program.

“It’s important to note that eDNA doesn’t mean bighead or silver carp are in Bubbly Creek, or that a reproducing population exists above the electrical barriers,” Irons said.

The detections triggered a letter from Michigan’s Democrat U.S. Senators Gary Peters and Debbie Stabenow to the wildlife service and Army Corps of Engineers urging immediate electrofishing and netting efforts before the Nov. 4 planned start date.

“While we recognize that eDNA does not necessarily indicate the presence of live Asian carp, there is no reason for response actions to wait another three days, particularly when the samples that led to the findings were taken three weeks ago,” they wrote. “We would also ask that additional eDNA sampling be conducted upstream of the electric dispersal barriers.”

In May, Congress received a $778 million plan to block the fish from advancing further north by strengthening a choke-point lock and dam on the Des Plaines River near Joliet.

The so-called Brandon Road plan proposes a gauntlet of fortifications that include an electric barrier, a bubble barrier, acoustic deterrents and a flushing lock meant to reduce the chances Asian carp could reach Lake Michigan while still allowing barge traffic to transit the lock.

The pricey plan is considered a compromise between Illinois and Mississippi River shipping interests and other Great Lakes states and environmental groups, which have pushed for total hydrologic separation of the two regional watersheds.

The October detections are not the first Asian carp DNA hits north of the electric barriers. The wildlife service found a handful of detections in Lake Calumet this spring. Live fish have also been found north of the barriers. One bighead carp was found in Lake Calumet in 2010 and one silver carp was found in the Little Calumet River in 2017.

The Illinois DNR says the Asian carp leading edge remains stable about 47 mile south of Lake Michigan near Dresden Island in the Illinois River and intensive commercial fishing has drastically decreased the population density there over the past seven years.