Wollongong Harbour the site of second vessel sinking in a week

The 30-foot cruiser called Gee Tee had been tied up in the corner of the harbour when it began taking on water just before 7am on Tuesday, July 25.

It was the second vessel to sink in the waterway during the past week after a yacht sank on July 19.

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Early morning walkers noticed the cruiser going under and launched into action.

Debra Murphy was one of the people involved in the rescue, but praised "Tristan the hero" for his efforts.

"It was a bit before seven when we noticed the boat taking on water," she said.

"It was a brilliant community effort to get the man and his dog off the boat. The door was under water so he couldn't get out of it."

Barry and Tiberius, his small dog, were halfway out the window when Tristan came to their rescue.

He scrambled down the ladder and across the boat, first taking the dog and relaying it to another volunteer, before helping Barry to safety.

"One woman took her jumper off and gave it to Barry, someone else gave him some socks - it was just a wonderful community reaction," she said.

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Among the onlookers after the emergency was a man, who asked not to be named, whose boat is moored next to Gee Tee.

"This is the third time this boat has gone down. The last times it was brought back up, craned out, repaired and put back in," he said.

The man said the boat had been listing to its starboard (right) side since Sunday, July 23.

Click on the photos below to see more pictures of the sunken boat

Firefighters from Balgownie and Shellharbour were called to the sunken boat to erect floating booms to prevent the fuel leak from spreading.

"Fortunately it's [the boat] in the corner and the tide is advantageous for us. If the tide was going out it'd be spreading the pollution, but it's coming in so it's pushing it into the corner," Fire and Rescue NSW Inspector Andrew Erlik said.

NSW Maritime boating safety officer Luke Macdonald was called to the harbour to investigate.

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"We'll be investigating what happened to the boat and how it sank and liaise with the owner to remove it from the water," he said.

Mr Macdonald was unable to say if the boat was seaworthy or a fine would be issued.

"Any compliance action is only a last resort," he said.

A NSW Environment Protection Authority (EPA) spokesman said they attended the scene and will "continue to monitor the situation closely with other regulatory agencies".

More to come.

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