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Published: 24 September 2020   •   Media release

Murray–Darling Basin communities are anticipating a wet spring but are warned there is a significant risk of hypoxic blackwater events occurring particularly in New South Wales.

MDBA Executive Director of River Management, Andrew Reynolds said the first flush of water after a long drought can make blackwater events more likely, and all governments and water authorities were working together to manage the unfolding situation.   

"After three hot and dry years, floodplains across our river systems have a high load of leaf litter – much of which hasn't moved since 2016.

"The current weather pattern as well as the high chance of La Niña conditions in spring increases the risk of floods. We've already seen this happening in far-west New South Wales in the past week," said Mr Reynolds.

"When rains wash organic matter into waterways it can lead to hypoxic blackwater events, which suck the oxygen out of the water. Fish and other aquatic animals have difficulty surviving."

Hypoxic, or low oxygen, ‘blackwater' is a feature of lowland river systems, and occurs during flooding when organic material – sticks, leaves, bark and grass – is broken down in the flood water or washed off the floodplain into the river.

The last major hypoxic blackwater events in the southern inland valleys occurred in 2016.

Director of Water Planning Implementation for the Department of Planning, Industry and Environment, Allan Raine said NSW agencies are keeping a close eye on conditions and advises people who witness blackwater to notify the department.

"So far the only area we are seeing hypoxic blackwater occurring is in the Lachlan River at Booligal. This situation is likely to continue over the coming week, until higher flows from upstream reach this area or we experience cooler conditions," Mr Raine said.

"In many cases mitigation measures to resolve blackwater events are limited but water agencies will work together to determine if and when any management options are available."

Current watchpoints being monitored for potential blackwater events in NSW include:

  • Lachlan River downstream of Forbes
  • Murray River communities from Tocumwal to the South Australian border,
  • Murrumbidgee River downstream of Narrandera, including the Lowbidgee floodplain from Maude to Balranald
  • Edward Wakool system in the region of Deniliquin and Moulamein

To notify the department of potential blackwater events email or to report a fish kill call the NSW Fisheries Hotline on 1800 043 536.

Further information on blackwater can be found at


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