The commotion over the now likely invasion of Asian carp makes it timely to look at who these fish are and why they're a concern.
As the U.S. EPA notes, two species of Asian carp are of concern, bighead and silver. The EPA notes the fish "are a significant threat to the Great Lakes because they are large, extremely prolific, and consume vast amounts of food. They can weigh up to 100 pounds, and can grow to a length of more than four feet. They are well-suited to the climate of the Great Lakes region, which is similar to their native Asian habitats"
Might they disrupt the already troubled food web of the Great Lakes fishery? Perhaps. One fear is that they will gobble up the forage fish on which desirable Great Lakes sport fish, including salmon and lake trout, depend. There will probably be other effects.
The EPA page is generally excellent, but its discussion of how the carp came to the U.S. is clouded. There is no mention that EPA itself may have encouraged the introduction of the carp, as Eric Sharp suggests.
One commenter on a post I did elsewhere also raised an issue.
Bighead and silver carp did NOT originally escape during flooding of the early 90s. The first silver carp was captured from the wild in 1972! Bigheads were abundant in the late 1980s. There may have been some ponds that flooded in the '93 flood, but the only reason there “is agreement” that this happened is because it sounds logical to the uninformed and that it has been so often repeated in the media that it is common (although probably incorrect) knowledge. There was a farm that flooded later, on the Osage River, but that was after the fish were already well established. The most logical reason for the escape of bighead and silver carp is carelessness, not the capriciousness of mother nature.
U.S. Fish and Wildlife info page is here.