Invasive Species Alert: Protect The Places We Paddle

By Jeanne Scherer
Aquatic Invasive Species Outreach Specialist
UW Madison Division of Extension, Natural Resources Institute

With the discovery of two more invasive species found in Wisconsin waters, we thought it would be a good time to share the following info with other paddlers. Many of the creeks where they’ve been found are ones paddlers like you (and Miles Paddled) frequent. New Zealand mudsnails have been found in several creeks over the last few years, most recently in Token Creek in the Yahara Watershed. And the first discovery of European frogbit in our waters was made in late July in numerous Oconto County streams, ditches and wetlands.

Whether you paddle, fish or hunt in or around these streams, it’s important to take note of what you can do to help prevent the spread of invasives which affect these important ecosystems. Take a bit to read about these Wisconsin invasives as well as others and learn how you might be able to help prevent accidentally moving invasive species around. You never know what’s hitching a ride.

Wisconsin Aquatic Invasive Species

Thanks to the amazing landscape and waterways of Wisconsin, we can experience everything from foggy morning trapping or duck hunting at Horicon Marsh to whitewater kayaking on the Peshtigo River. We enjoy wetting our lines in southwestern county trout streams and kicking back on evening pontoon boat rides on the Wisconsin River. We also all have a role in protecting our wetlands, streams, and lakes from aquatic invasive species when we boat, paddle, hunt, or fish.

Unfortunately, this summer, Wisconsin DNR received news of two prohibited species in our streams. Something that might have been avoided if everyone who steps into them or launches a kayak thoroughly cleaned off their footwear, gear, and boats before going from one stream to another.

Already known in ten southern Wisconsin streams, two more discoveries of New Zealand mudsnails were found in Dane County. About the size of a grain of rice, they can reach densities of 500,000 per square meter and it only takes one to start a new population. Studies on some Western U.S streams have shown that the snail has the potential to affect their food chains. With shells that tend to be dark brown, they’re easy to miss without careful cleaning. Wisconsin DNR staff and other researchers are currently studying the impacts to our streams and monitoring for more locations.

Wisconsin Invasive Species

The first discovery of European frogbit in our waters was made in late July in numerous Oconto County streams, ditches and wetlands. It is a free-floating plant that forms dense mats of petite, lily pad-like leaves, the size of a quarter or smaller. Below the water surface, they are a tangle of stems and stolons. European frogbit can quickly make a stream impassible by foot or boat and impossible to fish. The leaves tend to be dark purple on the bottom. Monitoring to determine the full spread of the plants is ongoing along with removal. If you think you have found an invasive species to report or are interested in helping with monitoring, you can find your DNR and County contacts here.

Wisconsin Invasive Species

The arrival and spread of aquatic invasive species like these does not have to be inevitable. We know that boat launches and stream access points are often the first place that a new invasive plant or animal shows up before spreading throughout a system. Duck hunters, trappers, and paddlers can also move them easily on footwear and gear. Felt and removable soles are especially risky. Whether you are taking out a bass boat or a paddle board, cleaning off your watercraft and draining all water from it and gear before you leave a site is a key step in protection, especially if you’re planning to go to another lake, stream or wetland within less than a week.

It’s not just about seeds and snails you may see when you come out of the water. Disease and the larvae of some snails and mussels are invisible to the eye. Waders, boots, and water shoes can easily hide a tiny seed or mudsnail hitching a ride from a creek or river you just fished or boated. Carry a sturdy brush and a gallon sprayer of plain tap water in your vehicle to thoroughly clean off all the mud, plant material and any other debris. Recent research has shown that Formula 409 sprayed on gear, footwear, and watercraft can kill New Zealand mudsnails, especially if you leave it on for up to 10 minutes before rinsing. Do not rinse next to the lake or stream.

New Zealand Mudsnail Fact SheetView or Download the New Zealand mudsnails fact sheet here.


Invasive Species Paddlers May Encounter

These are some species paddlers might come across. You can learn more about them by searching them by common or scientific name on the WDNR website.

Curly-leaf pondweed
Curly-leaf pondweed can make paddling and fishing a pain when it’s thick early in the year! It dies back when the water starts to warm in a lake, but in a cold water stream may persist much of the season.

European frogbit (EFB)
It flowers but they don’t come out long enough to be seen usually. 
Look for petite, lily pad-like leaves the size of a quarter or smaller.

Flowering rush
Flowering rush can grow along the shore or well out into a channel, depending on depth. It blooms in late May-June.

New Zealand mudsnail (NZM)
Paddlers are most likely to come across this species in cold-water streams. Fun fact: there are several different clones around the world. I read that each has adapted to a particular environment. For example, we have a second clone in Wisconsin that’s in a couple Great Lakes areas. In New Zealand, some are in shallow areas of a lake while a second clone is in deeper parts of the lake. The rock in the photo is covered with New Zealand mudsnails. They’re nearly invisible when you first pick up a rock like this, but then you realize it feels almost prickly from the shells and start to notice the movement.

Purple loosestrife (PL)
Wisconsin has an active and well-tested Biocontrol program to help manage purple loosestrife with a beetle that only eats these plants. This reduces the use of chemicals plus the beetles can fly to patches that people can’t reach. The plants can be difficult to manage on rivers and stream that frequently flood because the beetles and their larvae may drown when they are in the soil to pupate or overwinter. The flowers are obvious from about mid-July through August. More information can be found on the biocontrol page.

Yellow flag iris
Yellow iris loves shorelines and shallow waters, choking out some areas. Without flowers it can be confused with the native blue flag iris. Blooms are really obvious in late spring through June.

For more information on about invasive species with more photos, ID characteristics, and how to get involved with monitoring efforts (like building a boot brush station or taking part in Project RED), we highly recommend visiting the River Alliance of Wisconsin’s Aquatic Invasive Species page.

Wisconsin River Alliance Aquatic Invasive Species Site


What you can do:

Always remember to follow these easy and required simple steps:

  • INSPECT gear for hitchhikers and sediments
  • REMOVE any attached plants, animals, and sediments
    • SCRUB and RINSE!
  • DRAIN water from all equipment
  • NEVER MOVE plants, animals and sediments from a waterbody
    • Except harvested fish which are considered dead by law when not held in water

Before visiting another site, do one of the following voluntary steps with your gear:

  • FREEZE it for eight hours OR
  • WASH it with 120⁰F water OR
  • SPRAY with Formula 409, letting it sit for up to 10 minutes before rinsing (This has not yet been shown as effective on invasive species other than New Zealand mudsnails)

Aquatic Invasive Species TipsView or Download the AIS Prevention Tip information card

You can also help the DNR’s monitoring of invasives by reporting them to DNR Invasive Species, ideally with a photo and as specific a location as possible like GPS coordinates, stream/road crossings, or put-in/take-out points. You can also use this map of Aquatic Invasive Species (AIS) contacts to look for regional (DNR AIS Coordinators) and county (partnering AIS Coordinators) people to notify instead.

Anyone using wetlands and stream areas should also check out The River Alliance’s Cold Water Angling page with more information on steps you can take.

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