Fire and Rescue NSW crews were called to the harbour just after 9.45am to reports the 40-foot yacht was taking water.

About 20 firefighters from Wollongong, Shellharbour and Warrawong attended the scene to pump the water out of the boat after the bilge pump stopped working. They also put out booms to contain any potential spill.

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The crews managed to keep the boat from sinking and it was refloated just after 11am.

The sinking yacht was spotted by another vessel owner and he raised the alarm.

Jess Arroyo, the partner of the yacht's owner, said the firefighters were "amazing, absolutely amazing".

She said it believed that the pump had stopped working possibly because someone had disrupted the power supply.

Ms Arroyo said they often had problems with people getting onto the boat at night, and just a month ago they experienced a break-in.

Another boat owner, who did not wish to be named, said his vessel had been broken into three times, the mooring rope had been cut, and the power had been turned off.

There was also an issue at the harbour with hoons doing burnouts of a nighttime, he said, and rubbish left around the site.

He said the yacht club had also been the target of burglars.

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His boat and the one that almost sunk yesterday together weighed 35 tonnes, he said.

"If they get away because someone took away the mooring ropes, you're not going to stop them - someone's going to get hurt," he said.

Yesterday's near-sinking came a little more than two weeks after another yacht did sink in the harbour.

A crane had to pull Bionicle Boy from the depths after it sank in its berth on Tuesday, March 23.

A bilge pump failure was also a factor in that incident, but it was unclear why this had happened.

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