The Lake Leelanau Lake Association (LLLA) is fortunate to be partnered with some of the top swimmer’s itch researchers in North America. As such, we are privy to the current state-of-knowledge regarding swimmer’s itch and new innovative ways in which it could be prevented.


It was discovered in 1928 that swimmer’s itch is caused by a parasite that cycles between waterfowl in its adult form and snails during its larval form. As it passes between natural hosts, humans can accidentally intercept the microscopic larvae of the parasite, otherwise known as cercariae, causing the uncomfortable symptoms that we know as swimmer’s itch (see diagram).

SI Cycle

This discovery has set about nearly a century-long quest for control and prevention of this common and troublesome malady. Attempts at killing the parasite in either the bird or snail hosts have been made to break its life cycle. However, these strategies have proven challenging, and have had unintended negative ecological consequences with limited effectiveness. For example, applying copper sulfate to kill the snail hosts kills all aquatic life forms and was shown to be ineffective at stopping swimmer’s itch in research conducted and published on South Lake Leelanau. Furthermore, a recent discovery (2021) has shown that there are more parasite hosts than previously thought, such as Canada geese, mergansers and mallards. While diversity is often celebrated as an ecological benefit, when it comes to swimmer’s itch, it makes it harder to control. This discovery has discredited attempts made to control swimmer’s itch at the lake-wide level.

Without the ability to control the swimmer’s itch causing parasite (otherwise known as the avian schistosome cercariae), efforts have now transitioned to the prevention of swimmer’s itch. There have also been new discoveries in how the cercariae move through the water. They emerge most abundantly in the morning and travel up to the water’s surface, and then can move around at the surface due to wind and current, often accumulating in shallow water when there are onshore winds. This information has helped researchers develop innovative prevention strategies that may be helpful to everyone. Shifting the paradigm from lake-wide control to individual prevention has now empowered everyone to swim itch free if proper strategies are employed.

Strategies to avoid swimmer’s itch include:

  • Wear a tight-fitting, full-body rash guard (check them out online - ocean bathers wear them often to prevent jellyfish stings)
    • Larvae don’t typically penetrate fabric and bonus: less sunscreen is necessary!
  • Swim later in the day
    • Larvae usually exit snails each morning and will die or be eaten during the day.
  • Avoid lounging in surface waters
    • Larvae migrate to the surface and can accumulate in shallow water.
  • Avoid onshore winds
    • Larvae move with the wind and can congregate near windward shores.
  • Towel off after swimming
    • Some larvae are sticky and can cling to skin when you exit the water.
  • Swim in deeper water if you are able
    • Larvae are released from shallow water snails so fewer are found in deeper water.
  • Employ a swim baffle*
    • Baffles show promise in diverting drifting larvae away from swim areas.
  • Skim the swim area surface*
    • Modified pool leaf rakes show promise in clearing a swim area of the larvae.
  • Try different creams & lotions
    • Various products claim to repel larvae from entering the skin.
  • Contact your lake association
    • They may have reporting tools available to avoid areas with recently reported cases. The Lake Leelanau Lake Association suggests using this reporting tool to see if others have reported cases nearby and to report your own case.

*Learn more about these methods below.

New Innovations to Prevent Swimmer’s Itch

In addition to these strategies, there are several innovative prevention methods that have been tested locally in Lake Leelanau and Glen Lake by our local biologists (Ron Reimink and Kelsey Froelich) and their partner at the University of Alberta, Dr. Patrick Hanington (the 2022 Parasitologist of the Year). Please note that these methods have been tested, but limited replications have not allowed for full scientific review.

Oil containment booms 

These oil containment booms are vertical borders employed to create square containment areas as designated swim areas. Snails can be removed by divers or snorkelers in a short amount of time (dependent on the size of the swim area). This removes the larval host of the parasite in this area and is effective at least for several days post-removal.

Alternatively, an individual boom running perpendicular to shore (such as alongside a dock) could protect a swimming area since the cercariae would accumulate on the windward side of the barrier. This success of using an individual boom, however, is more variable depending on the wind direction and change.

Oil Containment Boom + Vacuum Pump

If no divers or snorkelers are available to remove snails from the swim area designated by the oil containment booms, the top layer of water can be vacuumed up with a small water pump suspended on an inner tube with intake valves suspended near the water surface. This pump can be pulled back and forth across the entire containment area to eliminate any cercariae larvae in the water. Removal of cercariae larvae would need to happen on the day of swimming for this method to be effective, unless paired with snail removal to last several days. Since the larvae are very fragile, they are destroyed during this process and so the water can be discharged right back into the swim area.

Vacuum pump

Oil Containment Boom + Modified Leaf Skimmer

A simpler and less expensive option for cercariae management within a containment area is the use of a modified leaf skimmer, usually sold for pool maintenance. The skimmer can be retrofitted with a pool noodle along one edge for buoyancy, a pull rope in place of the rigid extension pole for pulling, and 20-nanometer mesh netting to replace the large leaf-trapping net which can trap cercariae.

Modified Leaf Skimmer

A remote-controlled leaf-skimming boat can also be modified by adding a 20 nanometer mesh netting.

Remote Leaf Skimmer

For the full report on these methods, please click here.

Researchers continue to develop and improve innovative methods for preventing swimmer’s itch, so stay tuned!


What can I do if I get swimmer's itch?

Itching may start from the time you are in the water up to a day later and will last for about a week, accompanied by a rash. If itching and rash are severe contact a doctor for treatment. Temporary relief may be achieved through taking over-the-counter antihistamines, using anti-itch creams/lotions, or soaking in oatmeal or Epsom salts baths.


If you get swimmer’s itch, please report it!

Click below to report your case, see if others have reported cases before you swim, and learn more.

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