Scientists say grass carp have invaded three of the Great Lakes and pose a significant environmental risk. But they say there's still time to prevent them from becoming established.
Grass carp are among four Asian carp species threatening to reach the lakes, where they could upend ecological systems and compete with native fish for food.
A U.S.-Canadian assessment released Friday says grass carp have been found in Lakes Erie, Michigan and Ontario. At least some are reproducing, although most are believed to be sterile.
It's uncertain how many are in the lakes or how far they've spread.
Grass carp eat huge amounts of aquatic plants that provide habitat and spawning grounds for other fish.
Study leaders say both nations should quickly develop strategies for halting the invasion.