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Highlights in this update

  • Rainfall during August boosted storage levels in several southern catchments
  • Despite welcome rainfall to date in 2020, drought conditions persist
  • BoM forecasts 60-80% chance of higher than average rainfall through spring
  • Spotlight story: Blackwater is an emerging risk at several locations in the Basin
Rainfall deciles for previous 24 month period, showing rainfall was well below average throughout the Basin


Rainfall deciles during August were mixed, with average levels recorded across much of the Basin, while a significant tract through the centre of the Basin recorded rainfall above average. Small, isolated regions received highest on record deciles.

This rainfall belies the longer-term data showing that deficiencies have affected almost all of the Murray–Darling Basin since early 2017, and are most extreme in northern and western catchments, along with the River Murray and many of its major tributaries.

The map to the left shows rainfall deciles for the previous 24 months, clearly demonstrating that overall rainfall throughout most of the Basin was below average to lowest on record for the period.

Despite welcome rain in many areas over the course of 2020 so far, the impact of the extended dry period is still being felt, particularly in the northern Basin where total water storage is currently below 25%. Further widespread rainfall at above average levels will be required for many regions to cease drought conditions and replenish depleted water storages.

Rainfall across the Basin for August 2020. Most of the Basin received between 10-100mm of rain.


Averaged across the Basin over August, rainfall was 8% above the mean.

Early in August the upper Lachlan, upper Murrumbidgee and lower Paroo catchments experienced the highest on record rainfall through isolated events. This was driven by a low pressure system moving down the eastern coast. The heaviest falls associated with this system occured outside of the Basin.

BoM rainfall deciles for August indicated a tract of above average rainfall extended east to west through the centre of the Basin. Victorian and northern Basin catchments recorded average rainfall.

Water storages and streamflow

Public water storages across the Basin were holding 11,778 GL (52% of capacity) as at 2 September 2020. This was up from 46% recorded on 5 August 2020.

This increase was predominantly due to significant inflows in the upper Lachlan and upper Murrumbidgee catchments, which were captured in Wyangala and Burrinjuck storages, respectively. Burrinjuck Dam storage increased by almost 40%, receiving 430 gigalitres of inflow in August – the dam’s fourth highest monthly total in 10 years.

For the northern Basin, storages at 2 September 2020 were 1,247 GL, or 24% of active capacity. This was only a minor increase from 20% at 5 August 2020.

Burrendong Dam in the Macquarie catchment gained 119 GL to 24 August, as a result of isolated rainfall in upper headwaters.

For the southern Basin, consistent average to above average rainfall continued to increase storage levels across the region.

Public storages in the southern Basin were holding 9,822 GL, or 60% of capacity, at 2 September 2020. This was up from 55% at 5 August.

Inflows from Victorian tributaries have fulfilled most downstream requirements, leading operators to reduce releases from upstream storages including Hume Dam, where releases  averaged 600 ML/d.

Unregulated flows in the Murray have aided the filling of Lake Victoria in the lead up to the peak demand period in summer. At 2 September the storage level was 95% of capacity.

Climate outlook - Spring 2020

Weather through September is forecast to be wetter than average, with the chance of exceeding median rainfall 60-80% across most of the Basin.

The forecast for September to November is greater than 80% chance of exceeding median rainfall for almost all southern and central basin catchments, with some northern-most catchments 75-80%.

Recent cooling of the surface of the tropical Pacific Ocean, changes in tropical weather patterns, and continued ocean cooling forecast by climate models suggest La Niña could become established in spring 2020. The Bureau's ENSO Outlook remains at La Niña ALERT. This means the chance of La Niña forming in 2020 is around 70%—roughly three times the average likelihood.

Summary of threats to water quality in the Basin

Water quality and salinity

Although the Basin is still in drought, recent rainfall, changing weather conditions and cooler temperatures have eased the number of threats to water quality in the Basin. It is expected that there will be very little change in current conditions over winter, however the MDBA and state authorities will 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.

Blue-green algae red/high alerts

New South Wales sites on RED alert for blue-green algae:

  • Nil

Victorian sites on HIGH alert for blue-green algae:

  • Lake Eildon
  • Tullaroop Reservoir (near Maryborough)

Bushfire water quality risks

Risk of contamination continues to decrease as catchments recover from severe bushfires.


Salinity levels across all measurement sites were relatively stable, and most sites were well below 800 E.C. throughout August. Unregulated flows from upstream through the Lower Lakes has significantly reduced the salinity level measured at Goolwa Barrage, falling from a weekly average of 3,810 EC to 1,320 EC  during the month.

Spotlight: Risk of blackwater and algae

As warmer weather approaches and temperatures increase, so do the risks of water quality issues in the Murray–Darling Basin. Current threats to water quality are summarised on our water quality page.

A forecast chance of high rainfall during spring and into summer will be a welcome boost to rivers, some of which have been at very low flow levels for many months, or even years. However, the first flush of water through a river after a dry period can sometimes adversely impact water quality.

When a build-up of leaves and other organic material is regularly washed into rivers, it releases tannins and other carbon compounds which can turn the water black, like tea. This effect is known as blackwater, and the increase in carbon supports the growth of aquatic life.

During prolonged drought, higher amounts of organic material can accumulate on dry floodplains. When rain washes large volumes of material into rivers and the water temperature gets warm, bacteria can quickly start stripping oxygen from the water as they consume the carbon. This creates hypoxic blackwater, which can have severe impacts on ecosystems and potentially cause fish deaths. You can learn more about this process by watching this animation.

The MDBA is working with state governments and other partners to better prepare for blackwater events, including alerting the public to potential locations, and participating in emergency response planning to better manage any issues which may arise.

Blue-green algae is a regular occurrence as temperatures increase and is likely to become a concern (including for human health) in some regions. As the threat of blue-green algae rises, regular water sampling is undertaken by water managers and alert levels and warnings provide guidance for water users. A red alert level warning means that people should not undertake recreational activities and avoid drinking or bathing in untreated water containing high levels of potentially toxic blue-green algae.

For regular updates on blue-green algae alerts, contact the relevant agency in your state or territory.

Image: Blackwater in the Murray mixing with flows from the Darling River (2011)