Murray-Darling Basin Authority executive director of river management Andrew Reynolds said the first flush of water after a long drought could make blackwater events more likely, and all governments and water authorities were working together to manage the unfolding situation.
Current watchpoints being monitored for potential blackwater events in NSW include Murray River communities from Tocumwal to the South Australian border and the Edward-Wakool system in the region of Deniliquin and Moulamein.
“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,” Mr Reynolds said.
“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 NSW in the past week.
“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 floodwater or washed off the floodplain into the river.
The last major hypoxic blackwater events in the southern inland valleys occurred in 2016.
NSW Department of Planning, Industry and Environment water planning implementation director Allan Raine said NSW agencies were keeping a close eye on conditions and advised 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,” Mr Raine said.
“This situation is likely to continue over the coming week, until higher flows from upstream reach this area or we experience cooler conditions.
“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.”
To notify the department of potential blackwater events email waterqualitydata@industry.nsw.gov.au or to report a fish kill call the NSW Fisheries Hotline on 1800 043 536.
More information on blackwater can be found at: industry.nsw.gov.au/water/allocations-availability/droughts-floods/drought-update/managing-drought-recovery
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