Water samples taken from Lake Alexandrina on 21 March showed “elevated levels of potentially harmful blue-green algae”.

Experts have warned residents and visitors to avoid ingestion and bodily contact with the water.

The affected area “covers all of Lake Alexandrina, including the Goolwa Channel,” said SA Health’s Principal Water Quality Adviser Dr David Cunliffe.

Lake Alexandrina is a popular destination for camping, boating, fishing and other recreational activities.

SA Health has warned against swimming and diving in the Lake, but the Coorong District Council said boating and fishing were safe provided extra care was taken to avoid ingestion.

It’s recommended that any fish caught are cleaned and gutted thoroughly to prevent contamination.

Alexandrina Council CEO Nigel Morris said visitors mainly came to the lake for boating and fishing.

“These are two of the most popular activities in this body of water so the water quality notice will mostly likely have a minimal impact on people coming to our region for those reasons,” he said.

Coorong District Council Mayor Paul Simmons said the warning was there to inform visitors.

“Perhaps a natural response is to not take undue risks,” he said. “We leave it with the appropriate authorities to handle and manage it.”

Some cyanobacteria, more commonly known as blue-green algae, is normal for bodies of water in the warmer months. However, it can form dense clusters on the surface of still, nutrient-rich waters and produce toxins which are hazardous to humans and animals.

“It’s a naturally occurring organism,” Dr Cunliffe said.

“We tend to see blue green algal blooms more frequently in summer.”

The species identified in Lake Alexandrina is not easily visible because it does not form the surface scum typically associated with blue-green algae.

“We haven’t seen this type of algae in these numbers in South Australia before,” Dr Cunliffe said.

Consumption of water contaminated with blue-green algae can cause nausea and vomiting, bloody diarrhoea, fever and headaches. Contact can cause local irritation on the skin, eyes, nose, ears and mouth.

SA Health recommended cleaning affected areas thoroughly and contacting your GP if symptoms develop and also warned pet owners to keep animals out of Lake Alexandrina as algae can attach to fur.

“We just have to wait out the bloom,” Dr Cunliffe said.

“The nutrient concentrations are supporting the growth.

“Preventive measures include trying to reduce nutrient inputs into the river system – but that’s a long-term strategy.”

SA Water said that local drinking water is safe and none is pumped from Lake Alexandrina.

It has not yet received any reports of illness associated with the outbreak.