You can't see them when you step out of the water after a swim, but boy can you feel them later.

Swimmer's itch (cercarial dermatitis)-also known as "duck itch" or "lake itch"-is microscopic parasites lurking in lake water, capable of causing a skin rash that's itchy, scratchy and uncomfortable.

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Symptoms of swimmer's itch include burning, tingling and itching of the infected skin. Small reddish pimples appear within 12 hours of exposure and, while some of the pimples may develop into small blisters.

The critter responsible for causing the annoying temporary rash is a flatworm with a complex life cycle. The worm begins in the intestinal lining of water animals such as ducks, geese, beaver and muskrat, according to the Minnesota DNR. The worms lay eggs inside the host animal and the animal excretes the eggs into the lake water.

The eggs then hatch and the parasites swim around in search of a snail, a second host. They live inside the snail until it releases them back into the water, where they seek yet another host. This is when they often come across a human and burrow into the skin. People aren't suitable hosts, and the parasite soon dies. But the itching is already underway, spurred by the body's immune system.

Recommendations include rinsing off immediately after spending time in the lake and drying off with a towel. Lakeshore property owners and lake-goers are also advised not to feed ducks, which also carry the parasites throughout the lake.

Should you seek treatment for swimmer's itch? Physician assistant Melisa Palmer, who cares for patients at the Essentia Health Urgent Care and Convenient Care Clinics in Baxter and Brainerd, says, "It will normally clear up on it's own, however to ease the discomfort use antihistamines, anti-itch cream or take an Epsom salt/baking soda bath. Seeking medical attention is necessary only when not alleviated by over-the-counter remedies."

Not everyone who comes in contact with the parasite reacts. Some people show no signs of swimmer's itch. But for those unlucky souls who do, the symptoms can be quite annoying - though ultimately harmless. Red welts are a telltale sign. So is the can't-stop-scratching feeling that can last for two to seven days.