The Menindee fish kills

The Menindee fish kills refers to three mass fish death events that occurred along a 40km stretch of the Lower Darling during the summer period between December 2018 and January 2019. The Menindee fish kills were highly unusual in the severity and impact it had on native fish species. Native fish species that were impacted included the Murray Cod, Silver Perch and Golden Perch. It is unknown exactly how many fish died in these fish kill events, however it is thought that at least over a million fish may have died.

The Menindee fish kills were the result of a combination of factors that occurred in the lead up to and during the 2018/2019 summer period. During this time there were long periods of extreme hot weather which led to the water layering. This meant that there was a layer of cooler low oxygen water near the riverbed and a layer of high oxygen water near the surface. This was followed by severe and sudden temperature drops due to the weather conditions. As a result, these two layers mixed and caused a depletion of oxygen throughout the river system.

At the time there was also a lack of flowing water due to low rainfalls, over-distribution of waters, and high evaporation. All of these elements led to the development of blue-green algal blooms within the river system. Blue-green algae produces harmful toxins that can have harmful effects on people, livestock and native wildlife.

The management and over-distribution of water served as a significant contributor to the Menindee fish kills. Water in the Darling River system is used for a variety of purposes including for domestic requirements, agricultural and mining use, and flood management. The water is also subject to water sharing as outlined in the Murray-Darling Basin Agreement.

These competing interests in the use of water in the Darling River system have led to an environmental strain on the river system. In 2014 and 2017, the Murray Darling Basin Authority (MDBA) ordered that the lakes be drained to meet the water needs of those downstream. This depletion of water led to the Darling River system environment being unable to successfully recover from draughts and severe weather conditions that had occurred during this period.

As a result of the severe weather conditions, over-distribution and management of water, the Darling River system suffered from the devastating Menindee fish kill event. It will take many years for the Darling River to recover and return to full health.