The past week's heavy rainfall is continuing to affect Illawarra beaches, with swimmers advised to exercise caution at all beaches in the region this week due to possible pollution.
From Friday, hazardous surf condition will also return to the region, with people advised to stay out of the water and avoid walking near surf-exposed areas.
On Thursday, Bulli Beach and Kiama were rated worst for water pollution, according to the NSW Office of Environment and Heritage.
At Bulli, brown stormwater flowing from Whartons Creek was visible, and - like many beaches in the region - large amounts of seaweed and debris lined the sand.
At all other beaches, swimmers were advised to "take care" with water pollution "possible".
"Due to the extreme wet weather conditions, stormwater pollution may be impacting all Illawarra ocean beaches," the Beachwatch website said.
"Check for signs of pollution such as discoloured water and floating debris, and always check with lifeguards for latest beach conditions."
As a general precaution, the OEH advises swimming at beaches in the Illawarra region should be avoided for up to one day after heavy rainfall or for as long as stormwater is present, due to the presence of "several sources of faecal contamination" at many of the beaches.
At Sydney's beaches, NSW Water has reported algae blooms at some beaches, "which may appear as green or brownish slicks at the water surface".
"As a precaution, direct contact with the algae should be avoided as it can cause skin and eye irritations," the Beachwatch website said.
"It is expected the algae blooms will dissipate with changes in tide and wind conditions."
Meantime, the Bureau of Meteorology has another hazardous surf warning in place for the entire NSW coast from midnight on Friday.
NSW Police Marine Area Command advises swimmers, rock fishers and boaters to heed the warning.