Cercarial dermatitis, also known as ‘swimmer's itch', is being attributed as the cause of an allergic rash suffered by two swimmers who took a dip at the southern end of Lake Taupo.

While the cause has not been confirmed, Medical Officer of Health Dr Jim Miller says it's a possible cause for the rash.

Two swimmers reported getting a rash after swimming at the southern end of Lake Taupo recently.

He says swimmer's itch is caused by exposure to tiny larvae or cercariae in the water, most commonly found in shallow and relatively warm areas.

The larvae can cause an allergic irritation of the skin which is generally minor and self-limiting, however, if the rash is extensive or does not improve for more than a few days, medical advice should be sought.

'Any irritation should run its course,” says Jim, 'but can usually be easily treated with soothing antihistamine or steroid creams. Always see your doctor if symptoms persist.

The larvae are part of the life cycle of parasitic worms, which involves ducks, other birds and snails.

'Swimmer's itch occurs when a film of cercariae-infested water dries on exposed skin and, for humans, is a case of being in the wrong place at the wrong time,” adds Jim.

The presence of the larvae is not something that is monitored, but risks can be reduced by avoiding shallow areas of water, particularly where there is vegetation and bird life.

Toi Te Ora has erected signage around the currently affected area advising the public.

Jim says: 'In the meantime, people should take a precautionary approach and avoid contact with areas of shallow water, particularly around vegetation and where birds are evident.

'Washing or showering with clean water and drying yourself off with a towel after swimming can also help.”