Swimming after heavy rain could make you sick, says Toi Te Ora Public Health.

In a statement, it said with heavy rain forecast for much of the Bay of Plenty and Lakes districts, the local Medical Officer of Health was reminding the public of the standard public health advice to always avoid swimming in streams, rivers and beaches for 48 hours after heavy rain.

"After heavy rain there is likely to be contamination from rural and urban run-off," Medical Officer of Health Dr Neil de Wet said.

"To avoid illnesses such as diarrhoea, vomiting, skin infections or ear infections, it's best to avoid swimming in rivers, streams, beaches, lakes and harbour areas for at least 48 hours after heavy rainfall events."