Invasive Spiny Water Flea Found in Trout Lake

New Invasive Species Confirmed in Trout Lake, Vilas County
BOULDER JUNCTION, WI – The aquatic invasive species known as spiny water flea has been confirmed in Trout Lake in Vilas County.
On September 22, 2014 a local fisherman noticed what he suspected were spiny water fleas attached to his gear. He collected specimens and contacted Carol Warden, an Aquatic Invasive Species Specialist at Trout Lake Station, the research lab of the UW-Madison’s Center for Limnology.

Carol Warden collecting plankton samples in a northern Wisconsin lake.
Carol Warden collecting plankton samples in a northern Wisconsin lake.

On September 23rd, UW Trout Lake researchers confirmed the invasion, pulling samples full of spiny water fleas (Bythotrephes longimanus) out of Trout Lake.
In Wisconsin, the spiny water flea is classified as a “prohibited invasive species,” meaning it is unlawful to transport, possess, transfer, or introduce it within the state. By attaching to boater and angler gear such as fishing lines, downriggers, anchor ropes, and nets, spiny water fleas can spread to new bodies of water. They can also be transported in bilge water, bait buckets, or live wells.
But individual adults are not the biggest concern, says Jake Vander Zanden, a professor at the UW-Madison Center for Limnology.
“The eggs are the problem,” Vander Zanden says. “Adults don’t survive long out of the water. But they lay eggs that fall to the sediment that survive for months and then hatch the following year. It would be easy for a boat anchor to pick up some mud from the bottom of an invaded lake and, if it’s not washed off, carry eggs into another lake.”
Spiny water fleas can be distinguished from other zooplankton by their exceptionally long tails. Photo: Jake Walsh
Spiny water fleas can be distinguished from other zooplankton by their exceptionally long tails. Photo: Jake Walsh

Spiny water fleas are bad news because they prey on other zooplankton species, like Daphnia, an important food source for native fishes. Not only does this remove food sources for juvenile fish, but small fish also have trouble eating spiny water fleas because of their long, spiny tails.
What’s more, spiny water fleas are bad for water quality, says Jake Walsh, a graduate student at the Center for Limnology. Walsh has spent years researching the impacts of spiny water fleas in Lake Mendota in Madison. In Lake Mendota, spiny water fleas eat the Daphnia that would otherwise be eating the algae, and that’s bad for clear water. “After the spiny water flea invasion was detected in 2009,” he says, “summer and fall Daphnia pulicaria populations were reduced by 93% and the average Secchi depth, a measure of water clarity, declined by a full meter.”
Spiny water fleas were first introduced to the Great Lakes region through ballast water from ocean-going ships traveling from Europe and Asia. In northern Wisconsin, they have been confirmed in Gile Flowage in Iron County, both Stormy and Star Lakes in Vilas County and Butternut Lake in Forest County. Spiny water fleas are also in the Yahara Chain of lakes in Dane County. A few lakes in the western UP of Michigan, like Lake Gogebic, are also home to spiny water fleas.
Random sampling by the Wisconsin DNR over recent years has found some good news. For example, Plum and Pioneer Lakes, both near Star Lake and Spectacle and Franklin Lakes, both near Butternut Lake, were found to not have signs of a spiny water flea invasion. The results of the Wisconsin DNR’s random sampling of lakes throughout Wisconsin are made available towards the end of each year.
Carol Warden says the recent discovery in Trout Lake highlights the power of engaged citizens. “It’s so important to have citizens who are aware and volunteers out there looking for things like this,” she says. “They can be our eyes and ears for when the DNR and the Center for Limnology can’t be out on the water.” Warden also says that the new discovery highlights the importance of continuing the many education and outreach programs, like Clean Boats Clean Waters, the DNR and partners statewide engage in.
With a beautiful weekend coming up, Northwoods lakes will be seeing a lot of boat traffic and an increased need for folks to be on the lookout for stowaways.
All boaters and anglers in Wisconsin are required by law to inspect their boats and equipment, remove any attached plants/animals, drain all water from boats/motors/equipment, and never move live fish or plants away from a water body. But with something as small and hardy as a spiny water flea egg, extra precaution is needed.
“Right now spiny water fleas are at their peak abundance and they’re making a ton of eggs,” says Jake Walsh. “Your boat and equipment should be completely dry for at least twenty four hours before being used in another lake to ensure that the eggs are killed. Special care should be taken for live wells and other areas of the boat where water tends to collect and persist for long periods of time.” The most effective way to dry boats, Walsh says, is to leave them in the sun and the open air until nothing remains damp and water contained inside the boat or motor has evaporated.
And pay special attention to your anchor and anchor lines, as muddy sediment will be chock full of those hardy eggs. In other words, if it’s brown, wash it down.
U.S. Geological Survey FAQ Sheet on spiny water flea –
Wisconsin DNR spiny water flea FAQ sheet –
And, more from the Vander Zanden Lab at UW-Madison –