Here are some helpful strategies to minimize the negative affects of swimmer's itch — from protecting yourself before you swim to large-scale lake management strategies.
These strategies can significantly reduce your risk of contracting swimmer's itch.
A thick application of mineral zinc oxide sunscreen (SPF 30+) creates a physical barrier on the skin. Zinc particles are too large for cercariae to navigate easily. Apply liberally to all exposed skin 15–30 minutes before entering the water.
Applied over the zinc sunscreen layer, petroleum jelly creates a water-resistant seal that is difficult for cercariae to penetrate. This dual-layer barrier strategy — zinc base + petroleum seal — is significantly more effective than either alone.
A tight-fitting wetsuit (especially a full suit with sealed wrists and ankles) is highly effective — cercariae have difficulty penetrating neoprene. Standard swim shirts or rash guards are not adequate; loose-fitting fabric leaves gaps at cuffs and necklines where cercariae can still reach skin. Wetsuits are the most reliable physical barrier available.
If other swimmers have already been in the water that day and are complaining of itching, that is a real-time signal that cercariae concentrations are high. Similarly, check our case reporting map for recent reports near your lake. Swimming in a known active outbreak area carries a high probability of exposure.
Cercariae are released most abundantly on warm, sunny days between 10am and 2pm. Early morning swims, evening swims, or swimming on cool/cloudy days carry lower risk. After a cold front, cercariae concentrations can drop significantly. Conversely, the first warm day after a cool spell often sees a surge in release.
Snails live in shallow, rocky or sandy lake bottoms — typically in water under 3–4 feet deep. They concentrate in protected coves and along natural shorelines. Swimming further from shore in deeper water reduces your exposure to freshly released cercariae. Children are especially at risk because they tend to play in the shallows.
Wind and wave action concentrate cercariae along the leeward (downwind) shoreline. On a windy day, the shore on the side the wind is blowing toward will have dramatically higher cercariae concentrations. If your beach is on the downwind side of the lake, swimmer's itch risk is substantially elevated on windy days.
Rinsing with a hose or outdoor shower immediately upon exiting can help wash off cercariae — ideally followed by the vigorous towel dry. Keep a garden hose or bucket of water at the dock for quick post-swim rinse. Even a few seconds of delay before toweling can reduce effectiveness.
For common varieties of swimmer's itch (goose, mallard, etc.), cercariae burrow into skin as water evaporates. Rubbing your skin briskly with a towel the moment you exit the water — before the water has time to dry — can mechanically remove cercariae before they penetrate. Important limitation: This is largely ineffective for the Merganser variety, which enters skin while you're still in the water.
Feeding ducks and geese encourages them to congregate and linger near swimming areas — dramatically increasing local fecal contamination and cercariae concentration. This one behavioral change can meaningfully reduce your exposure risk, especially at public beaches where waterfowl feeding is common.
Individual prevention protects you, but it doesn't fix an infected lake. These approaches address the root cause — reducing the parasite population lake-wide.
The most effective and ecologically responsible method, validated by peer-reviewed research. Summer relocation of waterfowl broods within the critical 24-day window (before ducklings begin shedding) dramatically reduces snail infection rates the following year.
Trained wildlife specialists trap waterfowl hen and duckling broods during the brief window when ducklings are still young (day 1–24 after hatching, typically June–July). Broods are relocated to lakes that do not have the relevant snail species — such as northern oligotrophic lakes or Lake Superior. Without the duckling shedding cycle, newly hatched snails are not infected, and the snail infection rate drops precipitously year over year.
In 2015, Higgins Lake had epidemic-level snail infection rates of 3%. After a single summer of brood relocation in 2016, infection rates fell to 0.28%. By 2017, they had dropped to 0.05% — a 98% total reduction. Cases of swimmer's itch in swimmers at a high-use beach showed a substantial corresponding decrease over two successive years. (Source: Blankespoor, C.L., Blankespoor, H.D., DeJong, R.J. PLOS ONE, February 2024.)
Historically the most commonly used method — copper sulfate kills snails in the treated area. It is allowed in many states (with permitting) and can provide temporary, localized relief. However, it is increasingly considered an outdated and ecologically problematic approach.
Copper sulfate (CuSO₄) is applied directly to lake water in areas where snail populations are concentrated — typically shallow, rocky nearshore zones. Copper ions are toxic to mollusks at relatively low concentrations, disrupting cellular respiration in snails and killing them within hours to days of exposure. The treatment is typically applied by boat, dispersing the chemical across the target area. Effects are localized to the treated zone only and do not address the underlying source of cercariae from infected waterfowl.
Copper sulfate only kills snails where it is directly applied. Wind and currents freely transport cercariae from untreated areas across the entire lake. Snail populations rebound quickly after treatment. Copper sulfate also harms many non-target aquatic organisms — including beneficial invertebrates, fish gill tissue, and aquatic plants — with long-term effects on lake ecology.
This method has not been tested or proven as an effective control strategy for swimmer's itch. Praziquantel is a well-established antiparasitic drug used in veterinary medicine. In theory, treating infected waterfowl with praziquantel could eliminate the parasite in birds — stopping shedding without relocation or lethal removal.
Praziquantel works by disrupting the parasite's cell membrane, causing paralysis and death of the schistosome worms living inside waterfowl. The drug is typically administered orally — either through medicated bait or direct dosing — and is rapidly absorbed, eliminating the parasitic burden in the treated bird. In theory, if all infected waterfowl on a lake could be successfully treated before they begin shedding cercariae, the snail infection cycle could be interrupted without relocation or lethal methods.
This approach has not been sufficiently tested in Merganser populations, and re-infection occurs continuously in lakes with established snail populations.