A birdwatcher has stumbled upon a 19th-century gold coin, thought to be worth thousands of dollars, at a popular camping spot in outback Western Australia.

Key points: Bunbury man Michael Cross found the rare coin at a popular camping spot in WA's Goldfields

Bunbury man Michael Cross found the rare coin at a popular camping spot in WA's Goldfields The coin is an 1865 Australian gold half sovereign, estimated to be worth up to $5,000

The coin is an 1865 Australian gold half sovereign, estimated to be worth up to $5,000 Mr Cross says it's not for sale and will keep it as a souvenir

Michael Cross was camping with friends near Leonora in the Goldfields when he decided to go birdwatching at Malcolm Dam.

Leonora is a popular spot for people to take a metal detector and fossick for gold, but Mr Cross, who lives in Bunbury, was only armed with a camera that morning.

"It's very dry up there at the moment, so birds do tend to congregate around permanent water," he said.

"I was walking back to the ute and I thought I saw a heap of old bottles.

"I was looking at the ground and I saw this gold coin just looking at me.

"It wouldn't have been 10 metres from the dam wall."

The coin is thought to be worth thousands of dollars. ( ABC South West: Kate Stephens )

Hiding in plain sight

The find is even more incredible considering the number of fossickers who camp there while prospecting in the Goldfields.

"For the last 30 years there would have been thousands and thousands of people camped on that dam wall," Mr Cross said.

"There's even a skip bin up there for campers, so the amount of traffic where this coin was, over the last any amount of years, would have been substantial.

"It's just beyond belief that this coin could be sitting on top of the ground, being as available as it was."

Malcolm Dam is a popular camping spot near Leonora. ( ABC Goldfields: Andy Tyndall )

The coin is an 1865 Australian gold half sovereign.

Andrew Crellin, a rare coin dealer, said it was one of around 62,000 made.

"It's definitely rare," he said.

"The gold half sovereign was the equivalent to the $2 coin ... it was the coin that people used on a day-to-day basis.

"The population in New South Wales at that time was very low, so it was a very low vintage."

It is unclear how long the coin had been on the ground, which Mr Crellin said made the find that much more unusual.

"To find one on the floor of a rare coin dealer in Fremantle would have been incredible, let alone out in the backlots of Leonora."

Leonora is a popular spot for fossickers. ( ABC Midwest Wheatbelt: Cecile O'Connor )

Straight to the pool room

In mint condition, Mr Crellin said, the half sovereign could be worth tens of thousands of dollars.

Mr Cross, however, said estimates he'd received for his coin were between $2,000 and $5,000.

Despite the price, it is not for sale.

"I certainly don't want to get rid of it — I wouldn't trade a coin for money," Mr Cross said.

"Maybe one of my grandkids will have it, but I'll just keep it as a souvenir piece and maybe a good conversation piece."