Parts of Australia's key Murray-Darling river food bowl may be beyond recovery unless a prolonged dry spell and political wrangling over water use ends by October, a leaked scientific report warned on Wednesday.
"There has been 10 years at least that people have said you have got to restore the environmental flows to the system if you wish to keep the natural assets. We have failed to do that," University of Adelaide ecologist David Paton told local radio.
The Murray-Darling river basin, an area the size of France and Germany, produces 41 percent of Australia's agriculture and provides $21 billion worth of agricultural exports to Asia and the Middle East, including rice, corn, grapes and dairy.
But the government wants to secure water supplies and repair ailing rivers with an A$13 billion (US$12.2 billion), 10-year water plan topped by a A$3 billion deal to buy river water back from irrigators.
The center-left Labor government of Prime Minister Kevin Rudd deferred consideration of a scientific report into the crisis facing the basin's lower reaches until a ministerial meeting with state counterparts in November.
But Paton and other ecologists say much of the river system could be virtually dead by then, with vegetation on the lower Murray lost and fish species driven to extinction.
The lower Murray, where vast wetlands and lakes meet the sea, is an important region for horticulture, vegetable and pasture cropping, as well as dairy farming.
Environment Minister Peter Garrett said the government was aware the situation in the region was critical, but negotiations to better manage water flows were "tough and difficult".
"Recognising the seriousness of what's happening in the lower Murray is something that is front of mind for this government," he told Reuters. "These are particularly difficult times for the Murray ... with such low inflows."
Australian Greens Senator Bob Brown accused the government of "environmental vandalism" for not acting with more urgency. "The government's missing in action when it comes to the greatest river system in this country and the urgent need for action," Brown said.
Australia, the driest inhabited continent on Earth, has been suffering more than seven years of drought, with water inflows into the nation's rivers at record lows and farmers facing tough restrictions on irrigation.
Climate scientists have warned the continent is suffering accelerated climate change, with temperatures expected to rise by about 1 degree Celsius by 2030 and rainfall forecast to decrease by up to 20 percent by 2070 in the most populous southeast.
Australia this week cut its wheat output forecast by nearly 9 percent after the return of dry weather during a crucial planting period dashed hopes for a record crop from the world's second-biggest exporter.