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Rashes reported in Helena-area swimmers could mean algal blooms — or a parasite

Centers for Disease Control and Prevention

The Montana Department of Environmental Quality has been receiving reports of harmful algal blooms after some swimmers around Helena experienced itching and rashes after going in the water.

DEQ has issued harmful algal bloom caution advisories for Canyon Ferry at the Duck Creek campground and boat launch, the Hellgate campground, Lake Helena and for the Hauser Reservoir causeway.

Harmful algal blooms are caused by an overgrowth of algae that can release toxins into the water. Hannah Riedl is a water quality specialist with DEQ

“If someone accidentally swims in water with a harmful algal bloom, probably the most common symptom is skin irritation, like itching, or a bit of a rash," said DEQ water quality specialist Hanna Riedl. "It's really the most concerning if that water is ingested."

Ingestion can cause nausea, vomiting and diarrhea, and can even be fatal for dogs and livestock. Riedl says to watch for strange coloring that can indicate a bloom, like blue staining on rocks.

“You're kind of just looking for that spilled paint appearance on the surface of the water, or a little thicker like pea soup," she said.

But there’s also a parasite that could be the culprit.

Rashes associated with harmful algal blooms can also come from cercarial dermatitis, commonly known as Swimmer’s Itch, is caused by a parasite that burrows into a swimmer’s skin where it dies, forming an itchy rash of red bumps. The parasite lives in the blood of hosts, often waterfowl like ducks, gulls or geese, which then transmit parasite eggs through their waste.

When that waste touches water, the eggs hatch microscopic larvae that will swim around looking for aquatic snails to infect.

“Swimmer's Itch is typically found in slow moving or stagnant water, where snails like hanging out," said Abbie Ebert, also a water quality specialist with DEQ.

Ebert says swimmers should be wary of areas with excessive waterfowl droppings, and report any signs of symptoms.

Anyone who thinks they’ve seen or swam in bloom or contracted Swimmer’s Itch can visit to report symptoms and find a list of sites where algal blooms have been reported.