Four species of nonindigenous Asian carp are expanding their range in U.S. waterways, resulting in a variety of concerns and problems. Three species-bighead, silver, and black carp-are of particular note, based on the perceived degree of environmental concern. Current controversy relates to what measures might be necessary and sufficient to prevent movement of Asian carp from the Mississippi River drainage into the Great Lakes through the Chicago Area Waterway System. Recent federal response and coordination measures direct actions to avoid the possibility of carp becoming established in the Great Lakes. These include ongoing studies of efforts to separate the two drainage basins. According to the Great Lakes Fishery Commission, Asian carp pose a significant threat to commercial and recreational fisheries of the Great Lakes. Asian carp populations could expand rapidly and change the composition of Great Lakes ecosystems. Native species could be harmed because Asian carp are likely to compete with them for food and modify their habitat. It has been widely reported that Great Lakes fisheries generate economic activity of approximately $7 billion annually. Although Asian carp introduction is likely to modify Great Lakes ecosystems and cause harm to fisheries, studies forecasting the extent of potential harm are not available. Therefore, it is not possible to provide estimates of potential changes in the regional economy or economic value (social welfare) by lake, species, or fishery. The locks and waterways of the Chicago Area Waterway System (CAWS) have been a focal point for those debating how to prevent Asian carp encroachment on the Great Lakes. The CAWS is the only navigable link between the Great Lakes and the Mississippi River, and many note the potential of these waterways to facilitate invasive species transfers from one basin to the other. The U.S. Army Corps of Engineers (Corps) constructed and is operating electrical barriers to prevent fish passage through these waterways. In light of indications that Asian carp may be present near the Great Lakes, beginning in FY2010 the Obama Administration increased federal funding to prevent fish encroachment and related damage. Part of this funding was spent by the Corps to explore options that would achieve "hydrologic separation" of the Great Lakes and Mississippi River drainage basins. In January 2014, the Corps released a study (known as the "GLMRIS" study) which outlined a number of potential options ranging from no action to more than $18 billion for complete hydrologic separation and related mitigation. After pressure from Congress, the Corps in August 2017 released a draft of the Brandon Road Lock and Dam study (i.e., a follow-up study to GLMRIS focusing on a specific project) and recommended a tentatively selected plan. The selected alternative involves nonstructural control, complex noise, an electric barrier, and other measures, which would cost over $275 million and take four years to complete. Since December 2010, Michigan and other Great Lakes states have filed a number of requests for court-ordered measures to stop the migration of invasive Asian carp toward Lake Michigan from the Mississippi River basin via the CAWS. The U.S. Supreme Court denied several motions for injunctions to force Illinois, the Corps, and the Metropolitan Water Reclamation District of Greater Chicago to take necessary measures to prevent the carp from entering Lake Michigan. Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin sought a separate order in federal district court seeking similar relief, which was also denied. Bills introduced in the 115th Congress would have required the Corps to release a draft version of the GLMRIS Brandon Road Study (which was subsequently released in August 2017). With the release of the study, some in Congress may wish to authorize its draft contents, or direct other actions by the Corps and other agencies to stem the further spread of Asian carp.