How did invasive carp get to the U.S.?

Bighead and silver carp were imported into the southeastern U.S. in the 1970s to remove algae and suspended matter out of catfish farm ponds and wastewater treatment ponds. Similarly, grass carp were imported to manage weeds in farm ponds. Black carp were likely imported with shipments of bighead, silver or grass carp. While the exact manner of release into the wild is still debated, it is widely believed during large flood events in the mid-1990s, some of the farm ponds overflowed their banks and invasive carp were released into local waterways in the Mississippi River Basin.

In the mid-1980s, a grass carp sterilization program was put in place to reduce the risk of introduced fish reproducing and reaching nuisance levels that would result in detrimental impacts. The sterilization program has worked to some extent, but fertile fish are still being captured in locations where only sterile fish introduction is authorized.