Basin in Brief

Weakening La Niña conditions have resulted in a shift towards average to below average rainfall across most of the Basin over the past 3-month period.

The rainfall deciles graphic to the left shows the areas of below average rainfall during this period, which are predominantly in north-western catchments of the Barwon–Darling, Paroo, Warrego, Macquarie–Castlereagh and western area of the Condamine–Balonne.

The map inset contrasts rainfall deciles over the previous 12-month period, where the majority of the Basin received above average to highest on record rainfall.

This demonstrates the impact of an ENSO-neutral pattern as the Basin moves towards the chance of dryer El Niño conditions later in the year.

Following the trend of recent months, all catchments in the Basin recorded rainfall during April, however most areas received less than 25 mm across the observed period.

Rainfall for the entire Basin averaged 27.5 mm, which is 29% below the mean.

Back-to-back low fronts during April brought heavier rainfall to southern catchments, and snowfall to elevated areas of Victoria, New South Wales and the Australian Capital Territory.

Highest falls were recorded at Charnwood in the north-west of the Australian Capital Territory (379 mm), with surrounding areas in the upper Murrumbidgee catchment recording around 100 millimetres. This was similar to the Ovens catchment in Victoria.

Areas with the lowest rainfall include Bollon in the Condamine–Balonne catchment (0.6 mm) and White Cliffs in the Barwon–Darling catchment (0.8 mm).

Storage levels across the Murray–Darling Basin have remained relatively consistent with previous months owing to persistent rainfall over recent months and low demand leading into winter.

As at 26 April total storage in the Basin was 20,007 GL (90%), with southern Basin storages increasing slightly to 90% of capacity. Northern Basin total storage increased to 94% despite lower than average rainfall in some catchments.

Water releases from Hume Dam in the upper Murray were recently increased to manage airspace (to minimise the impacts of future rainfall). Prior to this, releases were being made to meet downstream demands, however these demands are reducing as the irrigation season draws to a close.

Unregulated flows are continuing in the Murray system, including the Edward River but excluding the lower Darling (Baaka) where the release of water for the environment is helping improve water quality. Operations at Menindee Lakes continue to be adjusted in response to low dissolved oxygen levels downstream of the Main Weir.

Flows to South Australia decreased to an average of 25,300 ML per day and is forecast to continue falling. Current unregulated flow to South Australia means that no additional releases from upstream storages are required.

Flows through the Barrages remain unregulated to the Coorong and Murray Mouth.

The likelihood of water quality issues is gradually reducing as conditions become cooler. Basin rivers and storages are nutrient rich and conditions remain favourable for blue green algae outbreaks. In the lower Darling (Baaka) there is still a risk of low dissolved oxygen levels as floodwaters recede.

The Murray–Darling Basin Authority and state authorities monitor water quality conditions across the Basin year-round. 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

• Hypoxic blackwater: Hypoxic blackwater is no longer a significant risk in most systems as floodwaters have receded.
• Low dissolved oxygen: In the lower Darling (Baaka), dissolved oxygen levels generally remain near or above critical ecological thresholds.
• Blue-green algae: There is currently a risk of blue-green algae across most parts of the Murray–Darling Basin, particularly in New South Wales. For the latest information on blue-green algae alerts, contact the relevant state government contacts via the Getting information about current algal blooms page of our website.