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Stop Spiny campaign seeks to halt barbed invader

Spiny water fleas disrupt the aquatic food web and lead to a drop in walleye population.

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A spiny water flea rests on a finger. The tiny, nearly translucent aquatic invasive species lives in cool, deep waters and hitches a ride from one lake to another via fishing lines, ballast and mud, according to the Wisconsin Department of Natural Resources
Contributed / Minnesota Aquatic Invasive Species Research Center
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SUPERIOR — An invasive predator has gained a foothold in Lake Superior. It lurks in cool, deep water, ready to snag a line and hitch a ride. To stop it from spreading will take action from boaters, those recreating on the water and, especially, local fishermen, according to the Wisconsin Department of Natural Resources.

Less than an inch long and translucent in color, a spiny water flea can be pretty easy to miss. Put one under a microscope next to local zooplankton, however, and its huge size and long, barbed spine make it stand out.

Spiny water fleas entered the Great Lakes in ship ballast water from Europe. They were first found in Lake Superior in 1987, according to the DNR.

“Unfortunately, we do not have a good way to eradicate or control spiny water fleas once they infest a lake,” said Zach Stewart, natural resources specialist and aquatic invasive species coordinator for Douglas County.

Spiny water fleas disrupt the food web in waters they invade. They eat smaller zooplankton, competing with young fish for food. And young fish have trouble eating them due to their long, spiny tails. Research has shown that walleye tend to be smaller and less abundant in lakes with spiny water flea infestations, Stewart said. The tiny invaders can also reproduce asexually, with no males required, allowing populations to explode.


“All of these factors add up to one thing: we have to stop the spread of spiny water fleas or prevent them from getting into our local lakes in the first place,” Stewart said during a half-hour Stop Spiny talk Thursday, March 24.

To date, the only Douglas County lake where spiny water fleas have been detected — other than Lake Superior — is Whitefish Lake. They were found on the lake in 2006, according to the DNR, but have no longer been observed. The fact that the county’s lakes are, as yet, free of the invader is why Stewart is launching a four-county Stop Spiny campaign this year, covering Douglas, Ashland, Bayfield and Iron counties.

“It is not a lost cause — we can still prevent their arrival,” he said.

The same key strategies that work to prevent other aquatic invasive species from hitching a ride work on spiny water fleas.

“Clean, drain and dry all equipment,” Stewart said. “Never transport water, mud or spiny water fleas caught on fishing lines.”

Spiny water fleas clump along a fishing line. Cleaning off fishing line and gear is one key step to preventing the spread of the aquatic invasive species, according to the Wisconsin DNR.
Contributed / Minnesota Aquatic Invasive Species Research Center

The tiny, barbed invasives tend to get tangled on fishing line more often than downrigger cables or anchor ropes. Cleaning off fishing lines and tackle with a cloth can be a first line of defense against the spread of the spiny water flea. It is important not to transport mud from one lake or stream to another, as well, because that’s where resting spiny water flea eggs are laid.

The invaders have a foothold in the Great Lakes, but human action can prevent a secondary spread into local lakes and rivers. The spiny water flea dries out quickly, and can’t travel overland independently.

“Luckily, what this really comes down to is all the ways spiny water fleas move can be prevented with our aquatic invasive species basic action,” Stewart said. “We always want to be sure we are cleaning all our equipment before its next use; we are draining any water out of livewell, boat ballast tanks, bait buckets; and we are drying off all our equipment in our boating or fishing gear.


“And if we follow those three big basics, we can really make a big difference and prevent spiny water fleas from moving into new lakes in our area.”

A monitor shows a magnified spiny water flea next to native zooplankton during a presentation by the Minnesota Aquatic Invasive Species Research Center.
Contributed / Minnesota Aquatic Invasive Species Research Center

The aquatic invasive species coordinator is planning to take his message on the road. He is available to speak with organizations in the area, and plans to purchase and provide Stop Spiny cloths that can be used to clean fishing lines and gear. Stewart said he intends to network with other local outreach organizations, such as the Clean Boats, Clean Waters campaign, to raise awareness of the danger the spiny water flea poses.

For more information or to set up a presentation, contact Stewart at zach.stewart@douglascountywi.org or 715-395-1266. A 2021 version of his Stop Spiny talk is available on YouTube, as well. Visit the Wisconsin DNR or Minnesota Aquatic Invasive Species Resource Center websites for more information on the spiny water flea.

Maria Lockwood covers news in Douglas County, Wisconsin, for the Superior Telegram.
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