Minnesota Opinion: Avoid catches you don't want this fishing season

Anglers can be vigilant to stop the spread of invasive spiny water fleas

A glob of spiny water fleas that collected on fishing line. New research shows fishing line among the most likely pathways for the invasive species to gather and spread. Minnesota Sea Grant photo.
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With the fishing open now in Minnesota , half a million anglers will be wetting their lines, hoping to hook into everything from sunnies to walleye to northern pike.

But far too many will also catch spiny water fleas or other invasives that not only are icky (which actually may not be a technical term) but are either threatening or are already doing real harm to our lakes, rivers, and fisheries. Zebra mussels , starry stonewort , Eurasian water milfoil , Asian carp, and more have long been rampaging Minnesota’s waterways and one of our favorite recreational and relaxational pastimes.

And let’s not forget snakehead fish, which — like something out of a horror movie — can breathe out of water and move on land. See, icky.

The loudest alarm this spring, though, is being sounded for the spiny water flea , a zooplankton roughly the size of a grain of rice but which is able to eat and decimate the microscopic foods that young, native fish need to survive and grow. Walleye in lakes invaded by spiny water fleas are smaller and less abundant than walleye in uninvaded lakes, the University of Minnesota Aquatic Invasive Species Resource Center has found.

Because nobody wants smaller or fewer walleye, “Stopping the spread of spiny water fleas is a crucial step in protecting our lakes,” the center said in a statement this week.


To learn how to stop the spread, its researchers loaded up a couple boats with fishing gear and ran “real-world simulations” (likely interpretation: they went fishing) in spiny water flea-infested lakes.

“The findings showed that fishing lines were most likely to entangle spiny water fleas, but they also get caught on downrigger cables, bait buckets, and livewells,” the center reported. And the more spiny water fleas in a lake, the more likely the critters are to end up ensnared on fishing gear.

“However, they can also survive in residual water in your boat,” researcher Valerie Brady pointed out.

So here’s what every angler needs to do — on opening weekend and throughout the fishing season — to prevent any further spread of the slimy little critters: Drain all the water out of your boat after pulling it from a lake and wipe down all your gear, in particular fishing lines, reels, bait buckets, and livewells. And let it all dry thoroughly.

Vigilance will be needed to slow the spread — and we all know a bit about that, don’t we, after more than a year of COVID-19 precautions.

Spiny water flea numbers won’t peak until mid-summer, so, “Not seeing a spiny water flea on your line this coming weekend doesn’t mean the lake is not (or is no longer) invaded,” the center’s statement said. “Most anglers will encounter spiny water fleas in the form of a gelatinous clump stuck in the eyelet of their fishing pole or gathered on sinkers or lures in late June through mid-fall.”

Anglers need to be especially vigilant on waters already infested. In the Duluth area, that includes the St. Louis River, Fish Lake, the Cloquet River from Island Lake to the St. Louis River, Island Lake, Crooked Lake, and West Twin Lake and East Twin Lake south of Brookston.

It’s up to anglers because, “We don’t currently have any management options available to treat spiny water fleas, whether that be biological, chemical, or physical, short of draining the entire lake,” researcher Donn Branstrator said in the statement. “So the best approach to fighting this invasive species is to contain its range and prevent any future spread.”


The best approach is also a simple one. And Minnesota anglers already have proven their ability to do their part. Only 8% of our lakes have a verified aquatic invasive species, and anglers’ and boaters’ efforts to slow their spreads are working, officials said in a DUluth News Tribune Outdoors report in April 2020. Catchy reminders like "Stop Aquatic Hitchhikers" and "Clean, Drain, Dry and Dispose" have become ingrained, like life jackets, minnows, and sunscreen, the story said.

To those let’s add “Stop Spiny,” and let’s halt the spread of a truly icky and harmful invasive, the spiny water flea.


The University of Minnesota Aquatic Invasive Species Resource Center created a campaign called “Stop Spiny” to end the spread of the invasive spiny water flea. Go to to learn about the project and for a map of Minnesota lakes and other waters already invaded.

This Minnesota Opinion editorial is the opinion of the editorial board of the Duluth News Tribune.

Minnesota Opinion editorial
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Related Topics: FISHING
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