Several popular Sydney beaches, including the iconic Bondi, resembled scenes out of an apocalyptic film yesterady after an algae bloom turned the water blood red.
Patches of the red algae, a natural phenomenon that can be exacerbated by certain weather conditions, were sighted between Bondi Beach and Maroubra Beach.
Both Bondi Beach and Clovelly Beach were closed while authorities conducted tests in the water. Gordon's Bay was also closed due to the algal bloom.
Waverley head lifeguard Bruce Hopkins said the bloom was spotted drifting off the north side of Bondi Beach at around 6.30am.
"It has got quite a fishy smell to it,'' Mr Hopkins said.
"It can irritate some people's skin but generally not much more than that.''
Mr Hopkins said the bloom has a "reddy-purple'' tinge and sits on the surface like oil sheen.
Red algae was uncommon but not unheard of at Bondi, Mr Hopkins added.