Seeing through mud

Since the breaking of the millennium drought (~2010) the Edward/Kolety–Wakool system has experienced several large unregulated flow events that have resulted in hypoxic blackwater conditions throughout the system. On each of these occasions hypoxic blackwater has developed and Commonwealth environmental watering actions from Murray Irrigation Limited (MIL) canal escapes have been undertaken resulting in positive outcomes for aquatic biota.In spring and early summer 2022 unregulated flooding throughout the Murray catchment triggered the development of hypoxic blackwater conditions and resulted in localised mortality of fish and crustaceans. Commonwealth environmental water was delivered through spring and summer from 16 MIL irrigation escapes to create small refuges of higher dissolved oxygen for fish and other aquatic biota. Assessing the outcomes of environmental watering actions is important for real time management and to inform future watering actions. This requires monitoring methods that can rapidly determine outcomes of watering actions.

A concurrent contingency monitoring program was instigated to assess the environmental outcomes of the water delivery from two of the larger irrigation escapes; the Edward escape from Mulwala canal, and the Niemur escape from the Northern Branch canal.

As part of this monitoring we conducted a novel survey approach to monitor fish abundances and species composition associated with the environmental watering actions by point sampling the adjacent river reaches using a boat mounted hydroacoustic camera. Results showed significant decline in dissolved oxygen concentration as distance from the release point increased and a positive correlation between large-bodied fish abundance and proximity to the irrigation escape release point.

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