The highs and lows of floods in the River Murray

Dead and dying fish are not what people expect to see when the River Murray is in flood, but that is exactly what can happen when a flood leads to a blackwater event.

Download PDF here

Rob Freeman, Chief Executive of the Murray–Darling Basin Authority said; ‘The Murray–Darling Basin Authority is co-ordinating a monitoring program of blackwater to improve our understanding of the causes of blackwater and its effects’.

‘The water flows in the Murray–Darling Basin are complex and while flood waters can bring life back to a parched region, they sometimes bring undesirable consequences.’

‘Unfortunately these floods have caused a number of fish deaths, including in areas upstream and downstream of Robinvale’, said Mr Freeman.

These fish deaths appear to be associated with blackwater events occurring in the waters of the River Murray, in the Edward and Wakool river system and most recently in the Goulburn-Broken, Lower Darling Anabranch and Loddon rivers.

Measures to mitigate the event have been taken but it has not been possible to release even more water to dilute the blackwater event as most rivers are operating at full capacity or overbank. However, where possible, action has been taken as flooding recedes. This has occurred recently in the Goulburn River, where Living Murray environmental water has been released to improve water quality and provide suitable habitat for fish.

MDBA will continue to put out a weekly water quality update while these events continue.

Mr Freeman said ‘Despite the adverse consequences, we shouldn’t forget the benefits of high environmental flows which are having positive environmental impacts on plants and most animals by providing a welcome change after years of drought.

‘River red gums are showing vigorous growth and endangered waterbirds such as Great and Intermediate Egrets are breeding.’

Blackwater events are a natural occurrence in low-lying river systems. The severity and extent of this event is a result of widespread floods washing the large accumulation of organic material from years of drought into the rivers. The low dissolved oxygen levels have been exacerbated by higher temperature as the flooding has continued well into summer.

Better quality water is also being released into the Edward River near Deniliquin from the Mulwala Canal to mix with poorer quality water.

For more information contact the MDBA Media office at media@mdba.gov.au