Swimming to be avoided at several popular Sydney beaches due to high stormwater pollution

Photograph: Peter Pesta Photography/Getty Images

Sydneysiders reeling from a sweltering week have been urged to stay out of the water at several popular beaches across the city after authorities issued a stormwater pollution “red warning” on Friday.

“Some swim sites in Sydney and Central Coast regions may continue to be impacted by stormwater pollution,” the New South Wales government agency Beachwatch warned in a statement posted to X.

Twenty-six swimming spots had a red warning of high contamination levels as of 10am on Friday, including Balmoral Baths, Chiswick Baths, Woolwich Baths, Foreshores Beach, Frenchmans Bay, Rose Bay Beach, Murray Rose Pool, Hayes Street Beach, Narrabeen Lagoon, Northbridge Baths, Oatley Bay Baths, Parsley Bay and Tambourine Bay. A red warning means the water is unsuitable for swimming.

Flowing drains, open lagoons, odours, litter and debris are all signs of stormwater pollution swept into beaches or bays.

The alert comes after days of mugginess, with Sydney experiencing its highest dew point on record last Thursday, as well as days of heavy rain.

“We have seen abnormally humid conditions across quite a number of weeks,” Jordan Notara, a senior meteorologist from the Bureau of Meteorology, said.

This humidity has been “assisting with the potential for heavier showers”.

“As soon as we have some instability in the atmosphere, so things like fronts or generally warmer conditions, we are seeing that moisture released from the atmosphere and resulting in heavy showers,” Notara said.

Though temperatures are forecast to be high, with 32C expected on Sunday, humidity levels are forecast to decrease at the same time.

On the other side of the country, the Trichodesmium bacterium has been confirmed at Mullaloo beach in Western Australia after brown surface scum from the water was tested.

The bacterium is naturally occurring in Australian waters, often when waters are calm and when the water temperature are high. Where a bloom incident occurs, exposure to water can cause skin irritation, a WA Department of Water and Environmental Regulation spokesperson said.