Grass carp in Lake Erie

Photo: The Canadian Press

Researchers have fresh evidence that invasive grass carp are swimming and spawning near the mouth of a river that flows into Lake Erie.

Their next step is figuring out how to stop it from gaining a foothold and devouring wetland plants along the shoreline and underwater vegetation in the lake that shelters native fish.

Grass carp are one of four Asian carp species threatening the Great Lakes, but they're not as worrisome as the bighead and silver carp, which could devastate fish populations in the lakes.

While environmental groups and scientists have put much of their attention on preventing the bighead and silver carp from reaching the lakes, the grass carp already have been found in Lakes Erie, Michigan and Ontario.

Brought to the U.S. more than 50 years ago to control weed growth, they're still sold to pond owners. Some states now require that they be sterilized before being released. But recent surveys have found grass carp eggs in Great Lakes waterways. Some made their way into the lakes via rivers, while others were dumped into the waterways. The fish feed on aquatic plants, eating up to 90 pounds a day and damaging areas used by spawning fish and migrating birds. What is not known is how many are in the lakes and where they've spread.

It's believed there are still only a small number of grass carp in the lakes. But a report released by U.S. and Canadian researchers warned this year that if effective steps aren't taken, it's likely that the invasive fish will be established in lakes Erie, Huron, Michigan and Ontario within 10 years.