The long weir at Mildura is being removed to prepare for a Murray River flood next month.
The last time the weir was removed was in 2016.
Flood warnings are being issued up and down the Murray Valley.
Even without further La Nina-induced rain, the high flows are expected to peak at high levels.
The river's big dams at Hume and Dartmouth are both full and spilling.
The Murray-Darling Basin Authority this week warned people along the Mitta Mitta River to monitor water levels in the coming days and weeks.
Dartmouth, the river's biggest dam was 99 per cent full this week, and the Bureau of Meteorology's outlook to October indicates wetter than average conditions are likely to continue across south-east Australia.
The MDBA has been releasing water from Dartmouth since early August to create airspace in the dam, in advance of more inflows during spring.
"At this stage releases from Dartmouth Dam continue to be through the power station, although flows over the spillway are possible depending on future rainfall events," MDBA executive director of river management Andrew Reynolds said.
The Darling River at Bourke is expected to exceed the minor flood level this weekend.
A minor flood peak is expected during the third week of September when floodwater is expected to inundate low lying areas adjacent to the river.
The almost 100-year-old Mildura Weir comprises 24 steel trestles, each weighing almost 11 tonnes.
The trestles are designed to be winched from the river to allow the safe passage of flood water.
Mr Reynolds said the weir needed to be removed ahead of increased flows expected in arrive by mid-September.
"The work to remove the weir will start later this week or early next week but we will confirm the exact timing when we have a clearer picture of the rate and volume of the flows upstream and when they are expected to arrive at Mildura," Mr Reynolds said.
"As a rule, we remove the weir when flows are forecast to reach about 42 gigalitres per day, which is currently forecast to happen in the first two weeks of September."
It is expected to take about eight days to remove the weir.
Boats will be able to use the flooded river and not the adjacent Lock 11 for travel.
People living along the river have been warned to keep abreast of weather warnings.