Fish experts are worried about the Great Lakes. They say the sea lamprey is alive and well in Lake Erie. That could mean trouble for the native fish species in the lake.
Lamprey look like eels, and attach themselves to fish as parasites.
"They are a huge risk to the fisherman and the restoration of the fishery what we want to do is to protect the fish so they can get big enough to reproduce," said Marc Gaden, with the Great Lakes Fishery Commission.
Gaden said there are more in the lake now than when the alarm was first sounded in the 1970s.
"Right now Lake Erie is our hot spot. We have lamprey abundances in Lake Erie we think exceed the numbers of even before lamprey control began," Gaden said. "There is a huge spike in Lake Erie. We think they are coming from either the St. Clair River, Lake St Clair or the Detroit River."
Gaden said a special pesticide is used to kill lampreys. He added scientists need to find out how and where they are coming into Lake Erie.
According to the Ministry of Natural Resources, one lamprey can kill more than 18kg (40 lbs) of fish during their 12-20 month adult life stage. On average, only one in five fish will survive an attack from a sea lamprey.