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New Discoveries in Swimmer’s Itch

Education, News June 22, 2020 No Response

Prevention is the Key

“An ounce of prevention is worth a pound of cure” so the saying goes.  This certainly rings true for Swimmer’s Itch. Prevention is the key to itch free enjoyment of our waters.

Listed below are suggested preventative strategies based on GLA Swimmer’s Itch research on the behavior and life cycle of Swimmer’s Itch. If carefully employed, these methods will work to greatly reduce the total number of or even eliminate itch cases for an entire swim season. Please note that these strategies should be used together to be most effective at preventing Swimmer’s Itch.

  • Cover your skin with swimwear that covers the area you want to be itch free (SI rarely affects a person’s hands, feet, and face)
  • Towel off vigorously after swimming
  • Swim in the afternoon or early evening vs. morning
  • Do not swim when the wind is blowing onshore.
  • Do not swim/wade in shallow water without using prevention measures
  • Install a swim baffle in your swim area (two years of research indicates this works!)
  • Use a parasite skimmer (watch the video link below for more info)
  • Use a kid friendly wading or “kiddy pool” vs. using shoreline lake water for small kids to swim more safely and itch free.

Be aware that there is never a case, even using all these tactics, that Swimmer’s Itch risk can be reduced to zero. But there is so much we can do to have our best chance at preventing the itch. Check out this informative Swimmer’s Itch Prevention Video on what we learned from our 2017-2019 research and for more details about what you can do! And if you do experience Swimmer’s Itch, please click here to report a caseWith your help, we can monitor and track cases of Swimmer’s Itch —and progress in managing it.

Brief tutorial and history of Swimmer’s Itch

Cercarial larva is the parasite that causes Swimmer’s Itch on Glen Lake. (NOTE: there are multiple species of parasites that cause Swimmer’s Itch in Michigan.) Cercariae are shed by multiple snail species that are infected by parasites transmitted by avian hosts —such as the Common Merganser, Canada Geese and Mallard ducks.

Historically we tried to break the lifecycle of the parasite in one of the two hosts. We tried to kill the snails by copper sulfate treatment, but that was ineffective (snails repopulated after expiration of the two hours of chemical potency). However, this was the only treatment for more than 30 years, from the 1950s to the 1980s. We tried to remove and harass the resident mergansers which at the time were thought to be the exclusive avian hosts on our lake from the 1980’s-2019. Despite these efforts, numbers of mergansers and cases of swimmer’s itch increased, and we discovered through DNA testing that mergansers were not the exclusive SI hosts we had once thought them to be.

Where are we now?

The Glen Lake Association has a 30-plus year effort in the research and management of Swimmer’s Itch. Our research in the mid-’80s helped define the life-cycle of Swimmer’s Itch on Glen Lake, i.e., one snail species and one bird species. Research from 2017-2019 again revolutionized the scientific understanding of Swimmer’s Itch. Through use of DNA testing, multiple species of itch were identified (including a never before discovered species) cycling through multiple bird hosts in addition to the Common Merganser, all contributing to Swimmer’s Itch on Glen Lake. Given what we now know, it is clear that attempts to control Swimmer’s Itch by interrupting this complex life cycle are ineffective.

Given the newly understood, increasingly complex nature of Swimmer’s Itch and clear and overwhelming evidence that copper sulfate application and Merganser harassment, trapping and relocation are ineffective and even harmful, what is there left to do? The Glen Lake Association has learned and continues to make new discoveries that lead us to new approaches for combatting Swimmer’s Itch. The key to future success in our treatment of Swimmer’s Itch is to prevent humans from coming into contact with the Cercarial larva. Using what we have learned about the behavior of Swimmer’s Itch, we can arm our ourselves against exposure to the Itch.


Prevention is the key! Research has demonstrated that there are methods and technologies available to effectively control individual swimmer exposure to Swimmer’s Itch. But we need your help! Ongoing research including the use of data from Swimmer’s Itch case reporting will be keys to furthering our ability to protect against and prevent Swimmer’s Itch.

Watch an informative video about SI here.



75th Celebration Fundraising Campaign: Supporting our Watershed Scientist Position

Education, News June 18, 2020 No Response

It’s all about the water….

After 75 years, the Glen Lake Association is celebrating this impressive milestone with the same basic focus: protecting and preserving the water within the Glen Lake/ Crystal River Watershed.

To commemorate this accomplishment with an eye to the future, the GLA Board of Directors is announcing the “75th Celebration Campaign” now underway.

Contributions raised between now and our Annual Meeting date of August 6 will finance GLA’s Watershed Scientist position, currently held by Watershed Biologist Rob Karner.

The association’s 75th Campaign goal: $150,000. Please click here to donate. 

Thanks to the generosity of three investors, the 75th Campaign has been challenged to raise $75,000 which they will match dollar-for-dollar, doubling the impact of every gift.

“Over seven decades of caring about our water by many people has brought us to where we are today,” said GLA development chair, Lori Lyman. “Through sound management practices, cutting-edge research and support by boards, staff, and a long list of volunteers committed to saving this resource, GLA is known throughout the state and beyond. Despite this strong leadership and progressive programming, the challenges continue with more invasive species, increased pressure and use and changing environmental conditions. To save this cherished water, GLA needs to remain vigilant in its research and education efforts.”

Please help us by investing in the future of the GLA during this landmark year. Your support will enable GLA to continue to research and deploy environmental best practices resulting in protecting and preserving the unparalleled Glen Lake/ Crystal River Watershed.

New Discoveries in Swimmer’s Itch

Education, News June 8, 2020 No Response

It has been widely accepted by many Swimmer’s Itch scientists that once Common Mergansers (once thought to be the major player in Swimmer’s Itch on Glen Lake) were live trapped and ready for relocation, that the approved DNR relocation sites were “safe” places to set the trapped birds free. The Michigan Department of Natural Resources (DNR) approved relocation sites based on four principles:  

  • New area is not a good swim area;
  • Site is free of the snail species that carries the parasite that cycles through Common Mergansers;
  • Not a place where the DNR fisheries were planting fish;
  • Suitable for Common Merganser survival

The 2019 Swimmer’s Itch research has now confirmed that many of the relocation sites have been tested “positive” for the species of parasite that cycles through Common Mergansers! This is bad news for the Swimmer’s Itch control program because it likely means that relocating Glen Lake mergansers to relocation sites that already have the parasite will only increase—perhaps dramatically—the itch risk for swimmers near the relocation sites. This new discovery presents a new ethical dilemma for the GLA and other lake associations around the state that use live trapping strategies.

One would think that a simple solution to this dilemma would be to find new sites that meet the DNR criteria where the parasite is not present. This may be a solution, but in the opinion of the local experts, there are likely “no new sites” to be found. Also, new discoveries have shown that relocated mergansers travel up to 20 miles once they are set free. 

Old Assumptions, New Thinking

Just a few years ago, it was thought that almost all of itch-causing worms came from Common Mergansers, with other birds like Mallards and Canada Geese only minor contributors. It was standard thinking, therefore, to assume that removing Common Mergansers from Glen Lake would have a major impact on reducing itch risk.  

However, 2019’s research on Swimmer’s Itch shows that Mallards and Canada Geese contribute to the parasite load in percentages higher than imagined. The mix of Swimmer’s Itch parasites from all the birds collectively contributes to increasing itch risk.

New data also suggests that snail densities, which can directly impact itch risk, fluctuate significantly from year to year. For example, when certain species of snail densities are high and combined with high population densities of the bird host, then SI risk for that specific life cycle can be problematic in a given year and move to center stage while other life cycles either hold their own or diminish.  

What does this mean for Glen Lake and our lake-wide effort to control Swimmer’s Itch? One thing is certain, the life cycle that is dominant one year may play a minor role in the next year, depending on snail density fluctuations and changing bird populations. This is a complex issue, with Mother Nature throwing in all kinds of twists and turns that make lake-wide control not only difficult but perhaps unattainable.

GLA will continually update you with new information as we receive it.