One of the worst affected beaches, Clovelly in Sydney, reopened Friday, just in time for a predicted heatwave over the weekend.
"There is no sign of the red algal bloom that kept the beach closed from Tuesday to Thursday this week," the local council said, a sentiment echoed by other councils along the city's northern beaches.
"It is now safe to swim, at the moment," a Surf Life Saving NSW official told reporters.
"We'll continue to monitor the situation."
Aerial footage shot over parts of New South Wales and neighbouring Victoria state showed huge blooms of the oily red to pink scum this week, which has a fishy odour and can irritate the skin and eyes but is not dangerous to humans.
One of the most striking features was the way it glowed blue at night, earning it the nickname "sea sparkle".
The Sydney South Coast and Hunter Regional Algal Coordinating Committees said the blooms typically occur as a result of currents bringing cold, nutrient-rich water to the surface.