Murray-Darling Basin Authority tips day Dartmouth Dam will spill for first time in 26 years

After hovering at around 99 per cent capacity for four weeks, the largest water storage in the Murray-Darling Basin is expected to flow over the spillway after inflows from last weekend's rain.

Murray-Darling Basin Authority senior director of river management Joe Davis said water would to flow flowing over the Dartmouth Dam spillway at low rates and contribute minor flows to the Mitta Mitta River downstream, with water also still being released through the valves at the base of the dam.

"There has been plenty of local banter about the possibility of the spill, and I know people have been taking bets on when it might happen," Mr Davis said.

"To begin with, water is expected to trickle over the spillway before the flows build up.

"Given it's been such a long time since the last spill, we expect locals and tourists will be keen to visit Dartmouth, particularly over the school holidays.

"Please be courteous of others and take great care on the road up to the site and in the limited parking area."

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Since Dartmouth Dam was completed in 1979 it has physically spilled in four times, each in the 1990s, the last time being 26 years ago in 1996.

"Dartmouth Dam has been considered effectively full since early August when we started pre-releasing water from the dam to manage airspace," Mr Davis said.

"The flow of water over the spillway at this stage is not expected to impact on the height of the Mitta Mitta River downstream, with flows expected to remain within the river channel at Tallandoon."

During the spill in 1996, water flowed over the dam wall from September 30 to 24 November 24, with a peak flow of 19,600 megalitres per day, on October 4.

River operators work in close collaboration with the Bureau of Meteorology to ensure dam management is guided by up-to-date rainfall and inflow forecasts.

Jointly managed by the MDBA and Goulburn-Murray Water, Dartmouth Dam is the most upstream storage in the River Murray system and collects almost 10 per cent of the system's inflow.

The Mitta Mitta River flows from Dartmouth Dam into the Hume Dam storage, which is currently at almost 97 per cent capacity.

Communities who live, work or holiday near rivers or on a floodplain are reminded to be prepared for flooding.

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