When the waters of Bondi Beach turned tomato red on Tuesday morning due to some "algal" infection of the waters, it elicited two types of reactions from the people who witnessed it. One was fear. But the others who were more hard-core adventurous, took a dip into the red waters. Now health authorities are worried those who swam in the infected waters could be at risk.

A number of people swam into the waters of Bondi Beach, despite it being temporarily closed, probably curious as to what could happen to them when the red water gets into them or their skin.

On early Tuesday morning, noctiluca scintillans, a thick algal bloom commonly referred as "red tide" or "fire in the sea," started to wash up on towards the shores of Bondi Beach.

The algae was believed to have first started off at Bondi, then spread throughout the entire morning, eventually covering Wamberal on the Central Coast to Cronulla Beach in the city's south.

Although varied reports said getting exposed to the red bath sea waters may cause skin rashes and eye irritations, still experts warned it could elevate to severe health-related risks since a large number of fish have died from the occurrence.

"It is potentially dangerous, it produces toxins and varies from people to people," Fred Gurgel, a marine biologist, said in The Herald Sun.

"There are some possible risks to human health from red algae including skin rashes and eye irritation, and for this reason the beach will remain closed until the algae dissipates," a spokeswoman from Randwick Council said.

The algal infection of the sea waters could have been likely due to the rising and heating water temperatures, since summer is just around the corner in Australia. The movement in the ocean currents is another factor which could led to the upwelling of colder nutrient-rich water.

Authorities expect the pristine waters of Bondi Beach will return back to normal after a week.

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