As the torrential rain finally paused on Thursday, the task of cleaning up the city's waterways is being assessed.

A heaving mass of light brown foam had taken over the north end of Port Kembla Beach, with darker sediment lining the sand at the high-water mark.

While some people stood and filmed, others thought it was great fun.

Read more: Nitro Circus to go ahead despite the rain

"It's quite the spectacle," said Lisha Keane, from Port Kembla.

"My kids think it's a big foam party."

Perhaps not the kind of foam it's good to play in, sadly.

In Thirroul, a grey substance covered the beach almost completely, resembling charcoal or coal fines but without an obvious source of either nearby.

Wollongong City Council said all kinds of material had been washed on to beaches and it was following up reports related to Thirroul.

Wollongong's City Beach was among the worst hit by the erosion - scarping - from the sea. A council spokeswoman said it was the south-facing beaches which copped the worst of it, and the heavily scarped areas could be unsafe.

"There has been significant sand erosion on the city's south-facing beaches; Bulli, Woonona, Corrimal, Towradgi and City Beach," she said.

"The scarping - where waves and water run-off erode sections of sand to create areas with steep and dangerous drops - will be made safe as the weather improves.

"Right now, council is working on a plan to be able to bring heavy machinery onto the beach to make these areas safer. To do this, we need the seas and swell to drop, and to make sure we've got the right measures in place to manage the sensitive marine environment.

"This work is an urgent priority for council and we will carry it out as soon as it is safe to do so."

All of the city's 17 patrolled beaches remained closed, including beach accessways along the coast which were unsafe for pedestrians to access, the council said.

"We will continue to barricade affected walkways that may be damaged and our ocean lifeguards will erect warning signage and continue to provide safety advice to beach goers." the spokeswoman said.

"At this stage all 17 of council's patrolled beaches remain closed due to rainfall impacting on ocean water quality and hazardous sea conditions. We will continue to reassess the conditions across the week."

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