It’s flea and tick season … and that means its waterflea season, too. Daphnia and other zooplankton are grazing on tiny spring-green plants in the lakes of northern Minnesota. Their numbers will swell as days grow longer and warmer, providing an abundant food source for the minnows and fish fry gulping them down. Waterfleas are small but pivotal members of aquatic communities. However, a rogue species is giving the order Cladocera a bad name.

Spiny waterfleas (Bythotrephes longimanus) are one of the few predatory zooplankton and an invasive species in the Lake Superior region. Experts believe spiny waterfleas survived passages to the U.S. from Eurasia in the freshwater ballast of cargo ships. They’ve occupied Lake Superior for nearly two decades.

"Spiny waterfleas can spread when fishing gear becomes contaminated with egg-laden females," said Doug Jensen, coordinator of Minnesota Sea Grant’s aquatic invasive species program. Although the females might die between fishing trips, they might be carrying resting eggs that can begin a new infestation.

"Its like dry soup mix," said Jensen. "Just add water and you’ve got more spiny waterfleas. That’s why boaters and anglers need to be especially careful about cleaning their equipment before going from one lake to another."

In Minnesota, it is unlawful to transport aquatic invasive species or water from infested lakes on roads and highways.

Although a University of Minnesota Duluth researcher discovered populations of spiny waterfleas in the other lakes off the Gunflint Trail, a resident angler alerted the Minnesota Department of Natural Resources (MN DNR) to the Saganaga Lake infestation. Jensen said anglers often report new sightings.

About 10 miles north of Duluth, spiny waterfleas inhabit Island Lake, and have been reported in Fish Lake. They inexplicably disappeared after invading Boulder Lake. The spiny waterflea population in Lake Superior is less robust than in the other Great Lakes, but is presumably the source for Minnesota’s original inland invasions. The extent of Lake Superior’s infestation varies yearly based on water temperature.

To raise public awareness that aquatic invasive species like spiny waterfleas can travel with people on roadways, Jensen is promoting the Stop Aquatic Hitchhikers campaign in partnership with organizations and businesses.

"It’s especially important that people stay vigilant along transportation corridors like the Gunflint Trail," he said. "New campaign partners are always welcome."