A citizen report of suspected spiny waterfleas in Shagawa Lake, near Ely, has been confirmed by the Minnesota Department of Natural Resources (DNR). An angler fishing on the lake found spiny waterfleas attached to his fishing equipment and supplied a sample of the find to the Tower area fisheries staff. A DNR aquatic biologist recently made a positive identification.
Spiny waterflea, or Bythotrephes longimanus, is a small planktonic crustacean that disrupts the food web and competes with small fish as it forages on microscopic animal plankton such as daphnia. Because of its long tail spike, the spiny waterflea is not eaten by small fish.
“There are more than 50 waterbodies in Minnesota designated as infested with spiny waterfleas, and 12 of these have been confirmed,” said Rich Rezanka, DNR aquatic invasive species specialist. “It’s critical for anglers to remove spiny waterfleas from all equipment because their eggs can live out of water for more than 12 hours and be transported to other waters.”
The species reproduces by a process called parthenogenesis. Throughout the majority of the year, the species population is entirely female, which allows for rapid population growth. Microscopic spiny waterflea eggs are hardy and capable of overwintering in lakes, and their small size makes them an easy candidate for overland transfer in water or mud.
Upstream water, Burntside Lake, was designated as infested in 2010 when spiny waterfleas were discovered there. Shagawa Lake will now be added to the list of infested waters, and downstream water, Fall Lake, will also be designated as infested waters because it’s connected to Shagawa Lake and there’s a likelihood of infestation spread.
When populations are high, anglers can experience frustration with masses of spiny waterfleas clogging fishing and downrigging lines and other water equipment.
Recreationists on these lakes should look for infested waters signage at public accesses. Signage will allow people using the lakes to be aware of the finding and take additional precautions to prevent the inadvertent spread to other lakes. Due to the discovery of spiny waterflea, bait harvest for any purpose is prohibited in Shagawa and Fall lakes.
Anglers, boaters and other recreationists are reminded to remove all aquatic plants, zebra mussels, and other prohibited invasive species, drain water from all water equipment including portable bait containers, and drain bilges and livewells by removing the drain plug before leaving the boat landing.
More information about spiny waterfleas, how to inspect boats and other water-related equipment, and a current list of designated infested waters is available on DNR website.