Sydney, Oct 19 (IANS): All Sydney beaches reopened on Saturday after several were closed due to tar ball pollution.

Seven beaches in Sydney had been closed after thousands of mysterious ball-shaped debris washed ashore over several days starting on Tuesday.

The iconic Bondi Beach and several others reopened on Friday and the remaining beaches closed to bathers have been cleared to reopen on Saturday, Xinhua news agency reported.

The pollution prompted a major clean-up operation and investigation into the source of the pollution.

Testing conducted by the local Randwick City Council identified the debris as tar balls, which are formed when oil comes into contact with debris and water -- usually as the result of an oil spill or seepage at sea.

The maritime authority in the state of New South Wales (NSW) said on Saturday that, based on health advice, the substance was not highly toxic to humans.

"We can now confirm the balls are made up of fatty acids, chemicals consistent with those found in cleaning and cosmetic products, mixed with some fuel oil," Mark Hutchings, executive director of NSW Maritime, said in a statement.

"They are not harmful when on the ground, but should not be touched or picked up," he said.

Beachgoers have been advised to alert lifeguards if they see any of the balls.

The first balls were found at the popular Coogee Beach in Sydney's eastern suburbs on Tuesday, prompting its closure.

By Thursday seven beaches, including Bondi Beach, had been closed.

The Australian Associated Press reported that over 2,000 balls have been picked up from beaches since Tuesday.

The NSW government has not identified the source of the balls and no oil spills have been reported to authorities.

NSW Environment Minister Penny Sharpe said on Friday that the government would harshly punish those responsible.