The mighty Dartmouth Dam is expected to spill for the first time in 26 years on Thursday.
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Hundreds of people have already visited the dam over the past month hoping to see the spectacular rock spillway in action.
The Murray River's two biggest dams - Hume and Dartmouth - have been "creating air space" over the past month while sitting at 99 per cent capacity.
Recent rains across the Murray Valley in the past week are expected to provide the tipping point.
Murray-Darling Basin Authority's river management senior director Joe Davis said water would start flowing over the Dartmouth Dam spillway this week.
Mr Davis said the spill would be at low volumes 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.
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"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.
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.
Built as a drought reserve, it is the largest capacity dam in Victoria and the highest structure of its kind in Australia and stores almost four million megalitres of water.
"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 November 24, with a peak flow of 19,600 megalitres per day, on October 4.
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.
