A tiny snail thought to be extinct has been found by accident in Tasmania's yingina/Great Lake, after not being seen since the 1900s.
The Beddomeia tumida, a freshwater snail measuring around 4mm, was found as part of conservation monitoring of the lake by Entura, an arm of Hydro Tasmania.
The chance discovery in the Central Plateau lake was the first time the snail had been seen or recorded for more than 120 years.
Andy Taylor, an environmental scientist with Hydro Tasmania, said the snail was found by accident while the team was searching for another thought-to-be extinct species — the Great Lake giant freshwater limpet.
"It's been in the dark for quite some time now," he told Helen Shield on ABC Radio Hobart.
"There's very little known about the ecosystem [at Great Lake]. It's a fascinating and under-studied one.
"We'd really like to learn more about the snail and try and get a feel for its abundance."
The snail was listed as "critically endangered but possibly extinct" by the International Union for Conservation of Nature Red List and is only found at yingina/Great Lake.
An elusive snail
The limpet the team was searching for was discovered during a survey when the lake was at a historic low in 2015 and 2016, and researchers returned and found it again last year while the lake was full.
Late last year, they sourced old roof tiles from the tip shop along with ropes and buoys to drop into the lake between 2 and 10 metres to see if any limpets or other bottom-dwelling creatures would latch on and call the tiles home.
Within 10 days they not only found the limpet, but the elusive snail as well.
Entura water quality consultant Kevin Macfarlane led the survey and said so far 15 snails had been found.
"Once we get an idea of the population size it could potentially be listed as not critically endangered, and hopefully we find that it's abundant," he said.
"As Beddomeia species are not present at locations of reduced water quality. This tells us that the water quality is very good, and the habitat is very good.
'Minuscule' chance of finding snail
At first, Mr Macfarlane did not know what species the snail was when he pulled it up and had it formally identified by zoologist Dr Karen Richards from the environment department.
When he got the text to say it was the missing species, he said it was "really exciting".
"I was extremely happy," he said.
Mr Macfarlane said he had been trying to find the snail for nine years.
"We had hoped it was there and put effort into searching for it but couldn't find it," he said.
He said in the 1990s mollusc experts spent a lot of time trying to find the snail but were unsuccessful.
Great Lake is the second-largest natural lake in Australia and has been altered to a size of 176 square kilometres.
Mr Macfarlane put down 100 tiles on ropes throughout the lake, but finding anything was a needle in a haystack mission.
"The chances of one of these crawling onto it is minuscule," he said.
Given the record low levels in 2015–16, Mr Macfarlane said the lake's inhabitants must be very resilient.
Surveys have also discovered other undescribed snail species, sponges, an aquatic plant, and a herb that resembles clover that had not been seen for 20 years.
The lake was the first source of water for Hydro Tasmania and was dammed in 1901, which made its levels rise.
It initially fed Waddamana Power Station, which was run by the state-owned Hydroelectric Department from 1916 until 1964, and was replaced by Poatina Power Station in 1966.
