You might not know it from the muddy surface, but our rivers and waterways can be a gold mine for antique bottle collectors.

Over the past four years Newcastle-based Tony Strazzari and Paul Szerenga have amassed an enormous collection of rare collectables, by scuba diving under the old bridges and wharves that once dotted the countryside.

"It's right along the lines of treasure hunting, it's not gold, it's not silver, but it's certainly history and something unique," Mr Szerenga said, while preparing to dive in the Patterson River at the historic village of Hinton.

"This area is lucrative because the Victoria Hotel is behind us and the old steamships used to pull up at the wharves that were lined along the bank here.

"So the blokes loading the boats, the children hanging around back in the day, drank their drinks here and often threw the bottles into the river."

Bottle collectors Tony Strazzari and Paul Szerenga about to head into the Paterson River at Hinton, NSW. ( ABC News Newcastle: Ben Millington )

Rare finds from the 1800s

Wonky black glass bottles, sometimes referred to as "pirate bottles", date back to the early 1800s. ( ABC News Newcastle: Ben Millington )

Many of the bottles found date back to 1800s, from convict-era clay ginger beer bottles to heavily embossed soda bottles with a marble stopper.

A particular favourite are the black glass bottles, sometimes referred to as "pirate bottles" for their misshapen wonkiness, that often held beer with a cork in the top.

"A lot of the old black glass is very, very old, it's early settlement type stuff, so 1820s, 1830s," Mr Strazzari said.

"They were all hand blown and every bottle's different, two bottles that came out of the same mould can look completely different.

"They're works of art, it's not like mass-produced rubbish that we drink out of these days."

Dive by feel in zero visibility

At the Paterson River in Hinton the pair spend an hour underwater on the first of three dives for the day, picking over the bottom of the riverbed in zero visibility.

Clay bottles from the 1800s. The grey bottle is a rare convict-era ginger beer bottle. ( ABC News Newcastle: Ben Millington )

Mr Strazzari feels around with gloves on his hands, shifting and moving and pulling apart the large amounts of timber and rubbish that has been dumped in the river over the years.

"I have accidently grabbed a mud crab who wasn't very happy and bit me," he said.

Mr Szerenga has his own technique, tapping and scraping away with a long metal stick listening for contact with glass.

Neither men have much of an idea of what they've collected until they reach the surface.

For Mr Strazzari it's a bag of "breakages and disappointment", but Mr Szerenga has found an embossed soda bottle from the 1880s, complete with its original stick-stopper.

"This is what you do it for, being the next person to hang onto this is a special feeling," he said.

"The young child who had this, popped the stick in it and finished the contents to throw it away, and then me being the next person to get it, that's really exciting."

"There's a gap in the history there of 150 years."