EVER since they started pumping water for their vines, the winegrowers of Langhorne Creek have learnt to cope with crises. But none as grave as the one they face now. Their water source at the mouth of the Murray River, in South Australia, has turned salty. Adelaide, the state capital 55km (34 miles) away, has been told its water supply from the Murray can no longer be guaranteed. The Murray Darling Basin Authority, a new body charged with saving Australia's biggest river system from expiring, has its work cut out.

Early last month Rob Freeman, the authority's boss, delivered grim news. The volume of water flowing into the Murray and its main tributary, the Darling, between January and March was the lowest in 117 years. The three-year volume up to March was the driest ever. Mr Freeman told Adelaide's 1m people this meant that not enough water might be conveyed down the Murray to meet their “critical human needs” next year. Just 17 years ago, Adelaide relied on the Murray for only 10% of its water: regular rains filling dams in the city's hills provided the rest. Now, it depends on the Murray for 90%.

Climate change and Australia's worst drought in a century are partly to blame. But the river system that covers two-thirds of Australia's irrigated farming land is also suffering from decades of overuse. South Australians feel this with growing bitterness. They are at the end of the line in a system that starts about 2,700km north. The more populous states of Queensland and New South Wales (NSW) comprise four-fifths of the basin's area. Farmers, especially cotton and rice growers in those upstream states, account for 83% of the basin's consumed water. The impact of all this has left the Murray's mouth near Langhorne Creek close to ruin.

The wine region's first water came from an ancient aquifer. Too much pumping forced the authorities in the early 1990s to switch water licences to the Murray, 10km away at Alexandrina, one of two lakes at the mouth facing the Southern Ocean. Plenty of water then flowed through the basin to keep the lakes fresh. Langhorne Creek's wineries boomed. A crunch came last year. The flows stopped, and Alexandrina's level has dropped 1.5 metres. Its water is now too saline to use.

The authorities are now pondering the harsh step of building a weir at nearby Wellington to stop the salt water moving back into the Murray itself. Experts predict this would in effect destroy the lakes and their surrounding freshwater wetlands. Penny Wong, the federal minister for climate change and water, says the “unfortunate reality” of the flow figures means the option must be kept as a “last resort”.

Growers at Langhorne Creek and nearby Currency Creek, meanwhile, have formed a company to build a pipeline to secure their water from a cleaner point on the Murray further east. They may yet survive. Australia's interstate water-trading scheme has allowed the state to buy water from distant farmers in NSW, who have switched to less thirsty crops, and keep it in store for Adelaide. Mr Freeman's body, launched by Canberra late last year, is the first with power to manage the entire river system, overriding rivalries between the four basin states, so that calamities such as Lake Alexandrina's don't happen.

Unless drought-breaking rains come, that will be a tough ask. Craig Willson, proprietor of Bremerton winery at Langhorne Creek, and a director of its pipeline company, reckons drought and loss of the lake's water have cut the region's productivity by almost 40% over the past two years. “Even so, we're surprised at how well some vines survive using less water,” he says. Applied to growers of other crops, the same lesson may help save the Murray.