. . .the Mary River turtle is endemic to south-east Queensland. Its population has fallen by more than 80% since the 1960s and its conservation status was upgraded from endangered to critically endangered last year.

Volunteers have worked for more than two decades at Tiaro, about 200km north of Brisbane, to save the species. The Mary River typically flows low at the start of summer – about 2 metres deep. But when Guardian Australia visited in December, it had surged above 10 metres after unusually heavy rain.

The result was the number of nests on the riverbanks – and the number of hatchlings that survived – was one of the lowest in the conservation program’s 24-year history. Seventeen nests, known as clutches, were laid during the season. Usually 30 to 40 are expected during the turtle’s breeding months of October, November and December.

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Eggs in nine clutches hatched successfully but eight were lost to flood waters. The head of the conservation effort and Tiaro Landcare project leader, Marilyn Connell, said the Mary River turtle already had “lots of things going against it, making it difficult to recover”.

“You sort of can’t believe it,” she said. “We felt despondent.”

The Mary River turtle’s formal listing of critically endangered means scientists consider it one rung away from extinction. The remaining wild population is estimated to be about 10,000. They face threats from foxes and other nest predators, invasive species and developments that disturb the flow of the river, including dams and weirs.

“Every year matters, that’s how we feel,” Connell said. “You just have to ask: how many of these bad years can a species that has already declined this much deal with?”