A POISONOUS plume of acid ''comparable to car batteries'' is forming in the Manning River, near Taree in northern NSW, researchers from the University of NSW say.
Swimming in and drinking water has been temporarily banned in sections of the river, while fish and other aquatic life are expected to be largely wiped out. The NSW government said it was working with Taree council to ''manage and reduce'' the problem.
The plume is being caused by floodwaters draining from agricultural land that had been reclaimed from wetlands, concentrating sulphuric acid in rivers.
''It is extremely acidic, comparable to car batteries,'' said a senior research fellow, William Glamore, from the University of NSW. ''You wouldn't want to touch it and you certainly wouldn't want to drink it because you'd probably have to go to hospital. If you are sampling it, putting your hand in the water, by the end of the day your skin is peeling off.''
Tests carried out by the university's water research laboratory show alarming amounts of acid, with a pH level of two - compared with a normal level of seven - meaning the Manning River water is roughly as acidic as lemon juice.
In the wake of floods, similar plumes of acidic water are likely to be growing in many other rivers along the east coast, as water drains from acid sulphate soils, Dr Glamore said.
The waters in the Manning River were also stained red by iron particles from the soil that had been flooded.
''We weren't actually testing for the effects on fish, but you can see that the river is essentially devoid of life,'' Dr Glamore said. ''The iron levels and aluminium levels are so high that anything that can swim out of the way does, and the rest dies. We saw eels gasping for breath.''
The Manning River, and other major rivers in the region, such as the Richmond and Clarence rivers, are flanked by farmland reclaimed from wetlands.
Acid sulphate exists in a benign state in waterlogged wetlands, but when these are drained to be turned into pastures it is exposed to oxygen and becomes sulphuric acid.
''Acid sulphate soils are well known to be a problem in this area of the state,'' said a spokesman for the NSW Office of Environment and Heritage. ''In this case Greater Taree Council are leading the effort to tackle the issue in the Manning.''
''This area is known to be one of the worst spots in NSW for this problem … Some of the solutions include the purchase and rehabilitation of the lands that are the cause of the acid run-off.''
The government estimates that, as a direct result of inappropriate drainage and excavation for urban development, enough acid sulphate soil has been created to generate 50,000 tonnes of sulphuric acid a year. It cost the NSW fishing industry up to $23 million a year, the department said.