WATER Minister Tim Holding has released figures showing declining inflows into Melbourne catchments in a bid to counter arguments against the north-south pipeline and the Wonthaggi desalination plant.

The figures show a record low of 3911 billion litres flowed into Melbourne's four major dams between 2000 and 2009, down from the previous decade low of 5033 billion litres in the 1980s.

However, a group protesting against the 70km pipe from the Goulburn River to Sugarloaf Reservoir says inflows in northern Victoria are also declining.

Mr Holding said water levels in the major catchments had fallen, "highlighting the need to diversify the state's water infrastructure and avoid relying solely on our dams".

Mr Holding came under fire last week after it was revealed Melbourne has enough water in its storages to last until the Wonthaggi desalination plant begins operating next year, if the city's storages receive only moderate inflows.

Anti-pipeline protesters and the Victorian Farmers Federation raised questions about the need for up to 75 billion litres to be pumped through the north-south pipeline augment Melbourne's supplies.

Plug the Pipe spokeswoman Jan Beer said the reduction in inflows was "happening to a greater extent in the northern catchments".

"How many years of reserve water does Mr Holding want for Melbourne, while here in the north people are still carting water, some rivers are not flowing and some people are on zero allocations?" she said.

Mr Holding said more than 80 per cent of the water savings from the Northern Victorian Infrastructure Renewal Program would remain in the north to be shared between irrigators and rivers.

However, Ms Beer questioned the amount of savings made by the irrigation upgrades.

"The irrigation losses have fallen," Ms Beer said.

"How will 80 per cent of the savings stay in the north if there's nothing to save?

"It's like comparing apples and oranges."

Figures from Goulburn Murray Water show Lake Eildon is 31 per cent full, up from 22 per cent this time last year.

Dartmouth is also faring better than the same time last year, at 30 per cent.

It was at 23 per cent capacity in January last year.