Two red swamp crayfish have been found in Tilde Lake in Clay County in northwestern Minnesota. It is the first time the invasive species have been confirmed in a Minnesota lake, according to the Department of Natural Resources.
The live specimens have been removed and DNR fisheries staff are searching the lake to see if there are others.
“Many aquarium animals and plants are invasive species that can cause serious harm if released into the wild,” said Heidi Wolf, DNR invasive species unit supervisor.
Wolf said the red swamp crayfish is a good example of a prohibited invasive species that some online retailers ship to unsuspecting teachers for classroom aquariums or to people hosting ‘crawfish boils.’
A permit is required to import crayfish – or almost any aquatic animals – for any purpose, and without a permit it is illegal to import or possess red swamp crayfish in Minnesota, she said. “We recommend people contact the DNR about legal alternative species.”
Red swamp crayfish compete with native species for habitat and eat tadpoles, snails and other small aquatic animals. Their burrowing habits make them extremely difficult to remove and cause damage to levees, dams and water control structures.
Prohibited species like red swamp crayfish cannot legally be possessed, released into the wild, used as bait, or transferred to others. The recommended and most humane method of disposing of them is to put them in a plastic bag in the freezer for a day, then put the bag into the trash.
“We recommend teachers check the prohibited invasive species list before committing to classroom aquarium animals,” Wolf said. “We also encourage teachers to discuss invasive species with their students.”
More information about prohibited and regulated species and what to do with them is available at