The Murrumbidgee river is dangerously degraded, infested with carp and its flows drastically reduced by dams, irrigation and climate change, a new report says.
The first comprehensive health check of Murray-Darling Basin river valleys found annual flows in the Murrumbidgee have dropped by 52 per cent.
The upper reaches of the Murrumbidgee which includes its Snowy Mountains headwaters and 41km flowing through the ACT are among the worst affected.
These sections of the river have few native fish or aquatic insects and are over-run by destructive alien species such as carp and rainbow trout.
Abnormalities such as tumours and heavy infestations of parasites were found in more than 8 per cent of fish caught in mountain waters of the river system, and 12 per cent of fish in Riverina lowlands.
The Murrumbidgee's main tributary, the Tumut, was also ranked as the worst affected by dam diversions of all rivers across the Murray-Darling Basin.
The audit mapped the ecological condition of 23 river valleys across the Murray-Darling Basin and found only one the Paroo in north-west NSW was in good health. Two river valleys (the Border and Condamine) were in moderate health, seven were rated as poor and 13, including the Murrumbidgee, were in very poor health.
The poor result for the Murrumbidgee valley includes data gathered from tests sites in the Queanbeyan, Yass and Cotter rivers.
The findings of the $2.5 million, three-year survey, which examined more than 96,000km of rivers and streams across the basin, was issued yesterday by the Murray-Darling Basin Commission.
The commission's chief executive, Wendy Craik, said the study found river valleys in the northern regions of the basin were generally healthier than those in the south. It also showed adverse ecological impacts were not ''simplistically cumulative from headwaters to the mouth of the Murray''.
Inlands Rivers network co-ordinator Amy Hankinson said the report's findings confirmed south-eastern Australia was facing an environmental crisis, requiring ''less reports and paperwork and more action to return water to stressed rivers''. The poor result for the Murrumbidgee was not surprising given the number of major dams and the amount of water extracted from the river for irrigation and urban use, she said.
''It's a smaller river than the Murray, and can't easily absorb the environmental impacts and intensity of water use.''
Ms Hankinson said the report's damning findings on river health across the Murray-Darling Basin showed state governments could not push ahead regardless with large-scale urban developments.
''We're already struggling to meet our urban water needs, and yet we're acting as if water will somehow be there for these new developments. It's time to change this urban planning mindset,'' she said.
University of Adelaide water economist Professor Mike Young said next month's Council of Australian Governments meeting in Sydney should commit to fixing the Murray-Darling Basin crisis within two years.
''We've had enough reports telling us how bad it is,'' Professor Young said. ''It's now time for governments to tackle the crisis decisively and equitably by ending the current complex and flawed water allocation system.
''It can be done quite simply by streamlining the allocation system to give the environment a formal entitlement.''
Professor Young said state and federal governments should agree to ''tear up or substantially amend'' the new Federal Water Act introduced last year by the Howard Government.
''It's fundamentally flawed by political compromise, it won't work,'' Professor Young said.
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