From this story on moneynews.com:
The aggressive Asian carp has reached the Great Lakes despite a government attempt to keep them out, according to a scientific report released Thursday. Researchers now believe the destructive species, which has been steadily moving northward for about 40 years, are now in southern Lake Michigan, putting at risk a sensitive ecosystems and a $7 billion fishing industry. The adaptable foreign fish outcompetes native fish species for food and habitat. "The most plausible explanation is still that there are some carp out there," Christopher Jerde of the University of Notre Dame, the report's lead author, told The Associated Press. "We can be cautiously optimistic . . . that we're not at the point where they'll start reproducing, spreading further and doing serious damage."