I had a reaction like this several years ago and we discussed the issue at length at that time. I found this information on the Arrowhead Lake Association's website http://www.ala-ca.org/mapper/itch:

Swimmer's Itch

Swimmer's Itch is a non-contagious skin rash that generally occurs during summer months in both fresh and salt water bodies around the world. It is an allergic reaction to a larval-stage parasite which is released by snails and causes a rash when it mistakenly penetrates a person's skin rather than it rightful host - usually a duck!

Swimmer's Itch is not a communicable or fatal disease. Only about one third of the people who come in contact with the parasite develop Swimmer's Itch.

If Swimmer's Itch develops, an infected individual will feel tingling, burning or itchy skin and soon develop a skin rash. A reaction can be noted within minutes or may be days later. Rash pimples or blisters, much like insect bites, may develop and increase in size over a 24-48 hour period. Itching, which can be severe, generally continues for up to a week or more but gradually decreases.

Children are most often infected due to their habits of swimming or wading in shallow water, because it appears that parasites may concentrate near shorelines. Moreover, children's skin may be more sensitive and prone to developing the rash.

To reduce your risk of exposure:

* Swim in water away from the shore.
* Avoid swimming near or wading in marshy areas.
* Briskly rub skin with a towel or shower immediately after swimming or wading.
* Don't encourage birds/ducks to stay near swimming areas by feeding them.

If a reaction occurs, rinse the affected skin lightly with isopropyl (rubbing) alcohol and then coat with calamine lotion. Try not to scratch to avoid a secondary infection.

Over-the-counter drugs are also available to reduce the effects. Antihistamines can be used to help relieve the itching while topical steroid creams may help to reduce the swelling. Before taking any of these drugs, however, consult your physician or dermatologist for advice.

Remember, Swimmer's Itch is caused by an allergic reaction. Therefore, if you develop Swimmer's Itch once, the more often you are exposed, the more likely you are to develop symptoms that are more severe and immediate after each exposure.