Under a 2007 mandate from Congress, the Army Corps of Engineers conducted a two-year study, called the Great Lakes and Mississippi River Interbasin Study, of the problem of Asian carp entering the Great Lakes via Chicago's web of waterways. Asian carp are known as a "nuisance species" that quickly gobbles up the plankton, thereby threatening the food source of the sport fish in the lakes. Conservation groups want the Corps to block the access ways as quickly as possible, but sports fishers and commercial shipping companies worry that the impact of blocking the flow of waterways will have on the lakes. The Corps' 210-page study estimates the cost of blocking the waterways at $18 billion.