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Highlights in this update

  • Rainfall was below average through April and May 2021 in the Murray–Darling Basin
  • Water storage levels increased in the northern and southern Basin
  • Above average rain expected for much of the Murray–Darling Basin during winter
  • Spotlight story: The Murray–Darling Basin Agreement
Rainfall deciles for April-May 2021


This graphic (left) represents average rainfall in the Basin for the past 2 months. It shows that rainfall across the Basin during April and May remained below average, with only small pockets reaching average levels or above average rainfall. This can be partly attributed to the breakdown of La Niña, which has come to an end, causing large-scale climate drivers to remain neutral.

Despite a decrease in rainfall during April and May, storage levels in the MurrayDarling Basin have continued to increase, now reaching 58%.

According to the Bureau of Meteorology, persistent, widespread, above average rainfall is still needed to provide relief from the impacts of long-term low rainfall.

Rainfall totals for the Murray-Darling Basin - May 2021

Rainfall and temperature

The Murray–Darling Basin experienced a significant contrast in rainfall during May. While the eastern Ranges received up to 50 mm of rain, the western catchments received about 5mm of falls.

In the northern Basin, Toowoomba experienced above average rainfall at 60.2 mm, while Cunnamulla recorded very low rainfall at 0.4 mm. Meanwhile, In the southern Basin, rainfall deciles along the River Murray were average to below average. Renmark in South Australia experienced below average rainfall recording 5 mm, while Albury in New South Wales experienced average rainfall recording 54.4 mm.

Temperatures were mainly average across the Murray–Darling Basin. However, parts of the southern Basin experienced above average temperatures. The hottest day in Victoria was recorded on 2 May 2021 at Hopetoun Airport where the temperature reached 29.4 °C.

In the northern Basin, above average temperatures occurred in some parts of Queensland, while northern New South Wales experienced below average temperatures. The coldest night in Queensland was recorded on 17 June 2021 at Stanthorpe Leslie Parade where the temperature dropped to -3.0 °C.

Summary water in MDB storages - 26 May 2021

Water storages and streamflow

Public water storages across the Basin were holding 12,815 GL (58%) as at 26 May 2021. This was an increase from 54% in April 2021.

Public storages in the northern Basin have remained steady and were holding 2,357 GL (50%). This is similar to late April 2021 when northern Basin storages were holding 2,331 GL (50%). This is a significant increase from early March when storages were holding 1,286 GL (27%).

Despite this, some public water storages in the northern Basin remained at 30% or below at 26 May 2021. In the Condamine–Balonne catchment, Cooby Creek reservoir was 19% while Lake Leslie was 29%. In the Namoi catchment, Split Rock Creek Reservoir was 30%.

Meanwhile, storages in the southern Basin increased. As at 26 May 2021, southern Basin storages were holding 9,592 GL (59%). This is a 5% increase from 28 April 2021 when storages in the southern Basin were 8,850 GL (54%) and an increase from the end of March 2021 when storages were 9,033 GL (55%).

In mid May 2021 the MDBA announced, that on behalf of the Basin state governments, small amounts of water from Menindee Lakes would be released in response to dry conditions in the southern Basin. As at 26 May 2021, Menindee Lakes was holding 999 GL (58%).

Climate outlook – Above average rainfall expected for winter

Winter rainfall is very likely to be above average across the MurrayDarling Basin. According to the Bureau of Meteorology, there is a greater than 80% chance of rainfall exceeding the median average from June to August. The bulk of the rain will occur in June with the wet signal in July remaining but tapering off.

Winter daytime temperature averages are also likely to be warmer than average for much of the southern Basin. This will mainly affect Victoria, south eastern News South Wales, and parts of South Australia. Meanwhile south western New South Wales and the northern Basin will experience average daytime temperatures.

The El Niño–Southern Oscillation (ENSO) remains neutral. Climate model outlooks indicate this neutral phase will last to at least October with little sign of El Niño or La Niña developing.

Summary of threats to water quality in the Basin - May 2021

Water quality

Water quality issues continue to be assessed, with a gradual decrease in blue-green algae and blackwater risk in line with seasonal expectations.

The MDBA and state authorities continue to monitor water quality across the Basin. For more information on water quality, and a map of threats, see the water quality page of our website.

Summary of key water quality issues

  • Blue-green algae (BGA): Many locations throughout the Basin are at risk of algal blooms. Although conditions have the potential to change rapidly, with low winter temperatures, the BGA risk will gradually reduce. For the latest information on blue-green algae alerts, contact the relevant state government contacts via the current algal blooms page of our website.
  • Low dissolved oxygen threat levels are reducing with improved flows through numerous catchments. Some low dissolved oxygen readings have been recorded at the head of the large flows in the Barwon–Darling rivers.
  • Bushfire contamination remains a possible threat in the upper Murrumbidgee, upper Murray and Ovens catchments following rainfall. This risk will lower as areas gradually recover from bushfire damage.

Spotlight: The Murray–Darling Basin Agreement

Last month the Murray–Darling Basin Authority (MDBA) began releasing small amounts of water from the Menindee Lakes. These releases started slowly to mimic natural river flows and provide connectivity between the Darling and Murray systems in response to recent dry conditions across the southern Basin. Sharing this water is part of the Murray–Darling Basin Agreement (the Agreement). 

The Murray–Darling Basin Agreement is a long-standing arrangement that aims to share water as agreed by the Basin states in the southern Basin and outlines the rules for the way the River Murray is managed and operated.

The MDBA is legally responsible for sharing water according to this agreement. It acts as an independent body to make sure each state gets the water it is entitled to from state tributary inflows and state tributary flows and the major River Murray storages (the Hume and Dartmouth Dams and Lake Victoria), and in some instances, water from the Menindee Lakes.

Water is not simply divided into 3 equal parts.

Victoria and New South Wales each receive:

  • 50% of water flowing into the Hume Dam
  • 50% of water flowing in the Kiewa River
  • 50% of water flowing into the Dartmouth Dam
  • 50% of water in the Menindee Lakes when they contain more than 640 gigalitres of water, at which point the MDBA has access to the lakes. When the amount of water falls below 480 gigalitres, only NSW receives water from them until they next reach 640 gigalitres.

South Australia receives at least 1,850 gigalitres of water in most years, except when there has been very low rainfall. Victoria and New South Wales each provide half of South Australia’s share from the water they have available.

The Murray–Darling Basin Authority has recently launched a new webinar series. The most recent webinar delved into and explained the Murray–Darling Basin Agreement and its elements. A special webinar was recently held about Menindee Lakes to share more information on the history of the lakes, the operational roles of governments and what happens when the water sharing arrangements between the states come into effect.

You can learn more about water sharing in the River Murray or view the MDBA’s webinar recordings.