Recent testing of waters near Lake Michigan has netted genetic evidence of the presence of Asian carp for a third consecutive year.

The U.S. Army Corps of Engineers reported 17 positive results of Asian carp environmental DNA (eDNA) from 114 water samples taken out of Lake Calumet and the Little Calumet River, both located on Chicago’s far South Side, late last month.

The findings were the strongest proof in two years of the existence of the invasive species within the Chicago area, according to USACE Fishery Biologist Kelly Baerwaldt, who said the results marked the highest number of positive hits for a single day since the agency began taking samples in 2009.

“This [result] has caused some questions because it is the highest proportion of positive hits we have received in one batch,” said Baerwaldt, who serves as Program Manager for the Corps’ eDNA monitoring program for the region. “But we don’t really know what that means – we don’t really know enough about eDNA yet to say whether 17 is more significant, or if it means more than say getting a few hits here and there, which we’ve typically been getting over the past  couple of years.”

The only actual sighting of an Asian carp in area waters occurred in 2010, when a bighead Asian carp was captured in Lake Calumet. Out of the eight varieties of Asian carp that have been imported outside of their native waters of China and Southeast Asia, silver and bighead Asian carp have been the most prominent in North America since being first introduced to the U.S. in the early 1970s.  

As Baerwaldt pointed out, all the genetic material collected since 2010 has been of the silver Asian carp, which has yet to have been seen in any of the Great Lakes, according to U.S. Geological Survey  data.

Despite the lack of actual sightings, Baerwaldt said the results of the water samples have caused the agency to step up its monitoring efforts.

“We’re really vigilant on the Chicago Area Waterway System – we really have a close eye on what’s going on,” Baerwaldt said. “Every time we get [DNA] results from one area, we go in there and fish and we can’t find anything.”

Reasons for the positive findings are still unclear, which prompted the Corps to conduct a two-year eDNA Calibration Study to give researchers a better idea as to how Asian carp genetic material is being transferred into areas where the actual fish have not been seen. Findings of the study are expected to be released by the end of 2013.

Baerwaldt said the agency is looking at possible factors that could explain how the genetic material of the Asian carp is being transferred, such as through the migration of fish-eating birds, or through waste water in storm sewers coming from Chinatown vendors, where Asian carp has been sold for years.

“We’re looking at these things, although these current incidents might be isolated, they do help tell us if there might be other things out there that can give us a positive result,” Baerwaldt said. “We want to determine whether it is [a cause] or if it is something we can cross off our list.”

Last month, USACE-designated group for handling Asian carp in Illinois, the Asian Carp Regional Coordinating Committee, released its annual Asian Carp Monitoring and Response Plan, which detailed the agency’s actions to prevent the fish from getting into the Great Lakes.

But the recent findings have further raised the concerns of some environmental groups, which say the results should serve as a warning call for the Corps to accelerate its efforts if they hope to have any chance of keeping invasive species such as Asian carp from establishing themselves in area waters.

“The eDNA is important because the implication is that the current tools being used to rebuff this invasion are inadequate,” said Natural Resource Defense Council spokesman Josh Mogerman. “This is just the continuation of an ongoing trend - we’ve had lots of these hits already.”

With 34 positive hits found in all of 2011, a finding that yielded 17 positive hits in the year’s first day of testing is a point of concern considering the Chicago Sanitary and Ship Canal provides direct access from the Mississippi River — where Asian carp prominently reside — to Lake Michigan.

Asian carp have been known as an invasive species along the southern parts of the Mississippi River for years, damaging ecosystems and local economies by starving out native fish species.  According to the U.S. National Oceanic and Atmospheric Administration, more than 65 million pounds of fish are harvested from the Great Lakes each year, generating more than $1 billion for local economies.

The threat to the local waterways has been such that it prompted U.S. Sen. Dick Durbin (D-IL) last year to co-sponsor a bill that would require the USACE to come up with a plan to create a barrier between the Mississippi River and Lake Michigan. Currently, the proposed legislation still awaits approval.