ANS Frequently Asked Question

Chicago District
Published Jan. 8, 2024

Frequently Asked Questions

What are you doing to prevent the spread of Asian carp?

The Corps is committed to sustaining our water resources and protecting our natural treasures, our Great Lakes.The Corps is a member of the Asian Carp Regional Coordinating Committee, which is comprised of various federal and state agencies with niche roles and responsibilities within the group. The ACRCC's goal is to prevent sustainable populations of the invasive fish from establishing in our Great Lakes. The Corps supports this goal through a four-part strategy: operating electric barriers; studying the effectiveness of the barriers and making adjustments, as necessary; monitoring the waterways to determine abundance and location of the fish; and a study looking at long-term prevention controls for the movement of several aquatic nuisance species of concern between the Great Lakes and Mississippi River basins via all potential aquatic pathways (GLMRIS).

Details about projects and programs being undertaken by ACRCC member organizations in the U.S. and Canada are outlined in the Asian Carp Control Strategy Framework document available on The frameworks are updated annually.

Where do you stand in the current Asian carp fight?

We are working tirelessly in the aquatic nuisance species and Asian carp fight and will continue to do so.

Currently, adult populations of Asian carp are about 47 miles from Lake Michigan and have not migrated for several years. We work with our partners to aggressively monitor the waterways to determine the abundance and location of these invasive fish. Monitoring methods include tracking tagged fish, using underwater cameras, netting, electrofishing and taking water samples to test for Asian carp DNA. The latest monitoring information is available at

The Corps will continue to work collaboratively to apply the best science, data and facts available to constantly improve the collective Asian carp monitoring effort.

The Corps is working on a new electric barrier, authorized by Congress as an upgrade to the demonstration barrier that has been operating since 2002. This barrier is scheduled to be activated in 2021.

While these on-the-ground efforts are in place, the Corps is also conducting a study looking at long-term prevention controls for the movement of several aquatic nuisance species of concern between the Great Lakes and Mississippi River basins via all potential aquatic pathways. These pathways include the direct Chicago Area Waterway System (CAWS) and 18 other sites that could become pathways during flooding. A report was submitted to Congress in January 2014 that outlines these controls.

How do the electric barriers work?

The electric barriers are operated to deter the inter-basin establishment of Asian carp and other fish through an electric field in the water. To create this electric field, steel electrodes are secured to the bottom of the canal. These electrodes are connected to a control building through electrical connections. Equipment in the control building generates a direct current pulse through the electrodes. 

Effective operation is dependent on a proper combination of the frequency, length and amplitude of the direct current (DC) pulses. We conduct studies and continue to monitor the Asian carp threat to ensure we are operating at the optimal settings.  Each barrier built takes lessons learned from the previous ones to ensure the most effective deterrence tool possible.

The barriers are complex electrical and mechanical systems and must periodically be powered down for maintenance. Therefore, more than one barrier is needed so that at least one barrier can be active when another barrier is being worked on.

Where are the barriers?

The barriers are in Romeoville, Ill. - about 37 miles downstream from Lake Michigan in the man-made Chicago Sanitary and Ship Canal. This location was chosen in close coordination with partner agencies. The construction of the canal was completed in the early 20th century to address sanitation and flooding. It allowed the reversal of the flow direction in the Chicago River and accommodated increased shipping but also allows for a continuous, direct connection for the transfer of aquatic nuisance species, like Asian carp. To our knowledge, our barriers are the largest of their kind in the world and the only on a highly-trafficked, commercially-navigable waterway. The barriers do not block the flow of water or the movement of vessels, so the canal can continue to serve its intended purposes for treated wastewater and stormwater management and navigation. The closest Asian carp population is about 10 miles further downstream, or 47 miles from Lake Michigan.

Do the barriers work?

We continually study the effectiveness of the barriers through studies and surveillance to include underwater cameras and tagged-fish studies. A total of 674 fish of all sizes have been tagged since 2010 in the CAWS. These fish have been detected over 29.1 million times. A total of two transmitters implanted into Common Carp downstream of the barriers have been located upstream although no detections were observed at barrier receivers. The most plausible explanation is assisted passage via barge entrainment; both transmitters were either expelled or the fish had expired. Only two Asian carp have been captured above the barriers toward Lake Michigan (in 2010 and 2017) during extensive monitoring. Each barrier built takes lessons learned from the previous ones to ensure the most effective deterrence tool possible. Ongoing testing is focused on determining optimal design and operating parameters for various fish sizes and given environmental conditions (such as water conductivity and temperature) and evaluating the potential impact of the movement of vessels through the CSSC on the effectiveness of the barriers. The Corps continues to work with their partners and stakeholders to assess the Asian carp threat and make informed decisions regarding barrier operations.

Where are the carp?

The inter-agency Monitoring and Response Work Group has documented adult Asian Bighead or Silver carp about 10 miles from the electric barriers and 47 miles from Lake Michigan in the Des Plaines River in the Dresden Island Pool. This population has not moved since 2006 and is considered the leading edge of Asian carp on the Illinois Waterway. No small Bighead or Silver carp have been observed closer than 70 miles from Lake Michigan.  The monitoring for Asian carp as well as the continued removal efforts of adult species near the leading edge continues to be a top priority of the Asian Carp Regional Coordinating Committee.



What is the Great Lakes and Mississippi River Interbasin Study (GLMRIS)?

Through Section 3061(d) of the Water Resources Development Act of 2007, Congress directed the Secretary of the Army, acting through the Chief of Engineers, to conduct a study evaluating a range of options and technologies available to prevent the transfer of aquatic nuisance species (ANS) between the Great Lakes and Mississippi River basins via aquatic pathways.

The Corps is conducting the study in consultation with other federal agencies, Native American tribes, state agencies, local governments and nongovernmental organizations.

The CAWS is Focus Area I of GLMRIS, as it is the primary, continuous aquatic connection between the Mississippi River basin and the Great Lakes.  Focus Area II is comprised of 18 pathways that have potential to become inter-basin transfer sites during flood events.   

Why is GLMRIS important?

Aquatic nuisance species threaten the diversity and abundance of native species; threaten the ecological stability of infested waters; or threaten the commercial, agricultural or recreational activities dependent on these waters.

What activities have been completed in GLMRIS?

  •  Inventory of current conditions (economic, environmental and social) and forecast future conditions within the study area;
  •  Identification of aquatic pathways that may exist between the Great Lakes and Mississippi River basins;
  • Inventory of current and future potential ANS;
  • Evaluation of possible ANS controls to prevent ANS transfer, to include hydrologic separation of the basins;
  • Analysis of impacts each ANS control may have on significant natural resources and existing and forecasted uses of the lakes and waterways within the study area;
  • Development of a report to provide Congress and other stakeholders with an analysis of potential ANS controls.

What is the GLMRIS Report?

The GLMRIS Report was submitted to Congress Jan. 6, 2014, and presents a range of options and technologies available to prevent the spread of ANS between the Great Lakes and Mississippi River basins through aquatic pathways. The report identifies eight alternative plans and evaluates the potential of these alternatives to control the inter-basin spread of 13 aquatic nuisance fish, algae, virus, crustaceans and plants in all life stages between the Great Lakes and Mississippi River basins. The options concentrate on the CAWS and include a wide spectrum of alternatives ranging from the continuation of current activities to the complete separation of the watersheds. Each plan includes a general location, conceptual designs, estimated implementation time and cost information.

The report is a product of the Congressional study authorization. Congress asked the Corps to evaluate a range of options and technologies available to prevent the spread of ANS transfer between the Great Lakes and Mississippi River basins via aquatic pathways.  The report outlines potential prevention methods and evaluation criteria.

The CAWS is the main subject of the GLMRIS Report.  In cooperation with state and local partners, additional progress has been made on other potential transfer points along the basin divide. More information on these sites can be found in the Focus Area II Appendix of the GLMRIS Report, as well as on the GLMRIS Website