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Wimmera CMA

Street Address:
24 Darlot Street, Horsham, 3400
(enter via Gleed St)

Postal Address:
PO Box 479, Horsham, VIC, 3402
Phone: (03) 5382 1544
Fax: (03) 5382 6076
Office Hours:
Monday to Friday, 8:30 - 5:00pm
(excluding Public Holidays and Christmas - New Year Closure.  Office may also be closed for short periods Monday mornings)


Water for the Environment update 2021 Autumn

May 18, 2021
WimmeraRiverBlackwater-360x253webBlackwater in the Wimmera River
WimmeraRiverBlackwaterPump-360x253webPumps helped aerate blackwater

Bouncing back from blackwater event

Wimmera update for Autumn

With last summer bringing La Niña conditions to eastern Australia, we wondered what was in store for the Wimmera. Intense rainfall events in December and January in isolated parts of the catchment led to the largest flows in the Wimmera River since the September 2016 floods.

The timing of the rain, warm summer conditions and a build-up of several years of eucalypts shedding bark and leaves getting washed into the river created an imperfect storm known as a BLACKWATER EVENT.

Most of the blackwater is now breaking down in large pools close to Dimboola and it is anticipated this will continue for several more months.

What is blackwater?

Blackwater conditions happen when a high concentration of organic matter and warm weather leads to a massive drop in dissolved oxygen in the water. This occurs as microbes busily work to break down the organic matter, consuming lots of oxygen in the process and tannins leach into the water, making it dark like tea.

They can lead to the death of fish and yabbies who suffocate from the lack of oxygen.

These events can linger for months and their impacts dissipate following cooler weather and long periods of flow.

Not all tea-coloured water in our waterways indicates low dissolved oxygen or blackwater events. Having organic matter in rivers provides carbon, which is vital for healthy waterway ecosystems.

Preparing for impacts

Blackwater events are a natural phenomenon in Australia and climate change modelling indicates that they are likely to become more common and severe into the future. There is no short-term solution to managing them but there are things we can do to reduce their severity.

Environmental water releases can create a source of oxygenated water to help prevent fish deaths but sometimes the flow rates and volumes available are insufficient to make a major difference.

Planting buffers of grasses and understorey plants alongside waterways can help filter water going into creeks and rivers.

Healthy water-plant communities in our waterways add oxygen.

Autumn flows

With several consecutive dry years and limited water availability, our focus is on protecting drought refuges. After Wimmera River flows in summer and early autumn reached Jeparit, instead of providing additional flows in autumn, the focus is on preserving water to deliver future flows, especially if conditions remain dry. 

There have been periodic low flows for MacKenzie River and Burnt Creek to Wonwondah to protect native fish, crayfish and platypus populations.

We’d love to hear from you!

We count on your eyes and ears to find out what’s happening in our waterways and we’re keen to hear about changes you have noticed. This helps us with future waterway plans and actions!

How to get in touch:

Autumn2021 Update Full Page