The Michigan Department of Natural Resources recently confirmed the presence of invasive red swamp crayfish in an outdoor muskellunge rearing pond at Wolf Lake State Fish Hatchery in Mattawan, Van Buren County, Michigan.

After stocking muskellunge in Thornapple Lake in Barry County and Lake Hudson in Lenawee County, hatchery staff found the carcasses of two unusual crayfish in the collection basket of Wolf Lake Hatchery Pond 20 (where the fish were reared) after the pond was drained. Crayfish traps were quickly deployed in Pond 20 and two adjacent ponds, resulting in the capture of one live, positively identified red swamp crayfish in Pond 20.

Though native to the southern U.S., red swamp crayfish have been prohibited in Michigan since 2014 and considered invasive in the state because of their ability to aggressively outcompete native crayfish for food and habitat, their high reproductive rate and their destructive burrowing along shorelines that can destabilize banks and infrastructure. Populations of red swamp crayfish were first detected in Michigan in 2017, with simultaneous discoveries in Sunset Lake in Kalamazoo and a drainage pond in Pontiac. To date, isolated infestations have been confirmed in Kalamazoo, Livingston, Macomb, Oakland, Van Buren and Wayne counties. Infestations are believed to result from the release or escape of aquarium pets, live bait or live crayfish brought to Michigan for crawfish boils.

Potentially affected lakes

Most fish stocked from Michigan’s state hatcheries are raised in tanks within hatchery buildings, inaccessible to outside species. Some fish, like muskellunge and walleye, are moved to outdoor rearing ponds to grow and improve survivability before being released.

The muskie sent to Thornapple Lake and Lake Hudson from Wolf Lake Hatchery in July were 12 to 13 inches in length, and each was individually handled and tagged before release, significantly reducing the likelihood that red swamp crayfish were transferred with them to the receiving waters.

Out of an abundance of caution, the DNR is developing a monitoring plan for both lakes and will alert lake users to report any sightings of the invasive crayfish.

Hatchery operations

The outdoor ponds at Wolf Lake State Fish Hatchery are sourced from well water, along with natural spring water that circulates through the ponds and is then released into a drain that eventually connects to the Paw Paw River.

According to Joe Mickevich, DNR southern area hatcheries manager, such an open system cannot easily prevent undesired species – including crayfish, tadpoles and even some small fish – from finding their way into the ponds, either over land or from bird and waterfowl movement.

When collecting fish from ponds for stocking at Wolf Lake Hatchery, the ponds are drained into the kettle, or collection box. Fish are netted from the collection box and loaded onto stocking units while staff attempt to remove as much bycatch, or undesired species, as possible. When needed, ponds are treated with rotenone, an aquatic pesticide, before the next use.

Response actions

While the source of the adult red swamp crayfish in Pond 20 is still unknown, Michigan’s Invasive Species Program staff is exploring several possibilities, including a known population 15 miles away, bait or aquarium release into the pond or nearby Wolf Lake, or accidental transport through forage fish used to feed the fish reared in Pond 20 but sourced from other states. The DNR and MISP are working together to determine the extent of the infestation and minimize the possibility of spreading the invasive crayfish to new locations.

• In the last week, 165 traps were set, spanning all 11 earthen bottom ponds at Wolf Lake Hatchery to determine the range of infestation at the site.
• The DNR is exploring the use of environmental DNA, or eDNA, to help determine the potential source, spread and presence of red swamp crayfish in the hatchery and surrounding waters.
• Suppliers and officials from states where minnows were sourced are fully cooperating with Michigan’s efforts to trace shipments and verify quality control measures to prevent contamination.
• Pending the results of trapping and assessment of risk, the DNR plans to explore potential control options at Wolf Lake Hatchery ponds, such as draining and drying ponds over the winter or adding pesticide, which has been used successfully on an experimental basis in some infested ponds in southeast Michigan.
• MISP and DNR staff are working to evaluate additional biosecurity measures, including improved screening of intake and outlet waters, additional screening methods to prevent bycatch from being transported with stocked fish and the use of only clean well water for fish transport.
• Wolf Lake Hatchery’s lined muskellunge ponds will be offline in 2026 for previously planned construction. Young muskie from this year’s harvest will be reared at Thompson State Fish Hatchery in Manistique, Michigan.

Because red swamp crayfish is a prohibited species in Michigan, it is illegal to knowingly possess, introduce, import, sell or offer the species for sale as a live organism, except under certain circumstances.

People can help prevent the spread of invasive species by knowing the laws, never releasing aquarium pets or plants into the wild, using bait only in the waters where it was captured and disposing of unused bait in the trash.

For more information on invasive red swamp crayfish, including identifying characteristics, visit Michigan.gov/Invasives. To report sightings of red swamp crayfish, collect and freeze a sample or take photos, note the location, and email information to Kathleen Quebedeaux, DNR Fisheries Division, QuebedeauxK@Michigan.gov.

Michigan's Invasive Species Program is cooperatively implemented by the Michigan departments of Agriculture and Rural Development; Environment, Great Lakes, and Energy; and Natural Resources.

Contact: Aaron Switzer, 231-383-2565, for hatchery information or Lucas Nathan, 517-599-9323, for invasive species information