A 30 per cent reduction in water use for irrigation across the river system was reported yesterday by the Australian Bureau of Statistics, despite a significant expansion of water use and irrigation farming in Queensland's part of the system.

The dire portrait of the Murray was released on the same day United Nations water adviser Maude Barlow criticised Victoria's plan to take water from the river system to Melbourne through the north-south pipeline.

Ms Barlow said the pipeline plan — which is projected to bring to Melbourne a third of water "saved" by irrigation upgrades in Northern Victoria — was the "worst thing" the Brumby Government could do.

"This is about the stupidest idea I've come across in a long, long time and I hear a lot of stupid ideas," she said.

A 30 per cent reduction in irrigation water use across the Murray-Darling system dwarfed the national decline, which was reported by the ABS to be 18 per cent in the year to June 2008.

That national figure — which saw irrigation water use at record lows — meant 2000 fewer irrigation businesses were in operation last financial year.

Once using two-thirds of all irrigation water in Australia, the Murray-Darling Basin now consumes just 50 per cent.

Victorian farmers have long been sceptical of the behaviour of Queensland farmers within the Murray-Darling Basin, with claims of unauthorised dams and diversions commonplace.

Queensland diverted more water into private dams last financial year than ever, and yesterday's report showed it had used 34 per cent more water for irrigation, and had expanded its irrigation areas by 61 per cent.

But National Farmers Federation natural resources manager Deb Kerr said Queensland's rising water use was influenced by the strong rainfall the state had had over recent years.