Diver Christopher Rantall was nearly five metres underwater near the city's breakwater when he eyed an unusual specimen partly lodged under reef and sand.

Mr Rantall volunteers weekly to clear rubbish from the seafloor and soon realised the object didn't belong among the rope, fishing wire and debris he normally collects.

After cleaning off heavy marine growth and worms he found a black purse. From its contents Mr Rantall believes the owner likely lost it as long ago as in 2007.

He's now using social media to reunite the purse with its owner, so far to no avail.

"They might have lost it while on the beach or it fell off the breakwater. With the tide it might have been lost anywhere, but it's obviously a local girl," Mr Rantall said.

"It would be interesting to find them. I know if I lost something, it would be cool for that person to have it returned."

Mr Rantall said the purse did not contain money, but held cards, an ambulance membership and even a membership to Warrnambool's Blockbuster video rental store, which closed in 2012.

There was also a well-preserved photo of a man, kept in a zip-lock bag.

"That was the most interesting thing in it, the photo is of a guy's head," Mr Rantall said.

"It is a bit of time capsule."

Mr Rantall has been diving for 25 years and posts his cleanup efforts on social media to promote a need to keep rubbish out of the ocean.

"The little bit that I pick up won't make much of a difference, but I can encourage people to be more mindful and be careful and just pick it up," he said.

The wallet was among his most interesting finds, Mr Rantall said, but he also discovered a stainless steel cup dated to 1944 and antique-looking wood he believes was likely from a shipwreck. He has since sought experts to identify the wood.

"It's well worn and has copper nails," Mr Rantall said.

"If it is of historical value it could be donated to a museum of some sort."

He said fishing items were common underwater near the breakwater, while he found household items such as tooth brushes, buttons and hair products near Shelley Beach.

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