Scientists on some of the heartland's great rivers are turning up ominous signs that Asian carp may be harming other fish, but the dire predictions that the carp would kill off other fish haven't been realized yet.
Bighead and silver carp have infested the Mississippi River and its tributaries for years. Government agencies have spent more than $150 million on technology to keep them from reaching the Great Lakes, where it's feared they could starve out other species.
Biologists said that so far, the worst hasn't yet happened on the Mississippi and Illinois rivers. There have been no extinctions or population crashes among native fish.
But studies have shown that bigmouth buffalo and gizzard shad are getting skinnier. Both are important species that eat the same food as Asian carp.
A new report released by Canada's Fisheries and Oceans ministry said Asian carp could find hospitable conditions in all five Great Lakes if they gain a foothold.
The report is based on a 16-month assessment of risk to the lakes from the invasive carp, which have infested the Mississippi River and many of its tributaries.
The analysis said it could take as few as 10 male and female pairs to establish a population in the lakes if they find good spawning areas. The report said more than 70 rivers across the Great Lakes could serve that purpose.