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Published: 17 December 2010   •   Media release

The Murray-Darling Basin Authority today advised of the 'blackwater' event 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.

The unprecedented December inflows are resulting in blackwater with low dissolved oxygen in many locations across the Murray region, and there is a risk of this moving downstream to South Australia in coming weeks. While blackwater is a natural occurrence in low-lying river systems, the severity and extent of this event is due to the prolonged drought and subsequent widespread flooding.

The Authority, with New South Wales and Victorian agencies have implemented several measures to lessen the impact of the blackwater. However, most rivers are currently operating at full channel capacity, preventing further dilution flows as a management option.

It is expected that the blackwater event will continue to affect the River Murray, Edward, Wakool river system, Loddon, Goulburn–Broken and Murrumbidgee rivers and the Lower Darling Anabranch over the coming weeks, and may worsen in some locations as water temperatures become warmer.

Fish deaths have been reported in several rivers, and Murray crays have been observed avoiding the blackwater. River users are reminded that it is currently a 'closed season' for Murray crays. It is also fish spawning season and anglers may wish to voluntarily limit their catch to minimise further impacts on native fish populations. Consumption of discoloured or outwardly stressed fish may be a health risk due to their poor condition.


More information about blackwater

Blackwater events occur as a natural phenomenon due to the rapid breakdown of leaf litter on the forest floor causing water discolouration. The breakdown of leaf litter plays an important ecological role as it provides nutrients back into the river system thereby promoting the growth of many aquatic organisms. However, at times such as now, this process can result in very low dissolved oxygen levels which can cause stress to fish, crayfish and other animals that breathe underwater, and if severe enough can result in fish deaths.

The recent floods have been very beneficial for the floodplain forests, wetlands and rivers, which have been coping through years of drought. However the drought over the past years has led to a build up of leaf litter on the floodplains, which has lead to development of the current blackwater event. This, combined with warmer water temperatures and even more flooding in early December has led to a very low dissolved oxygen level.

The MDBA and Victorian and NSW authorities are monitoring the water quality and also exploring options to manage any emerging problems from the blackwater event.

For more information contact the MDBA Media office on (02) 6279 0141 or media@mdba.gov.au

For NSW enquiries contact NSW Office of Water media: 0407 403 234

For Vic enquiries contact the Department of Sustainability and Environment: 0400 983 471

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