While some people pointed the finger at the Alcoa’s coal power station, which pumps pollutants into the air just behind the town, the explanation for the fish kill seems to be the heavy rain. The long drought had exposed coastal acid sulphate soils in Marshy and Salt Creeks, just upstream of the Anglesea River. The oxygen in the air reacted with the soils to create sulphuric acid, and the sudden arrival of rain sent it downstream into the Anglesea River.
Another possible explanation for dead fish in the Anglesea River is water extraction by Barwon Water, which may have caused groundwater levels to change, contributing to acidification. However the independent review of the fish kill event, released in October, wasn’t able to conclude if the extraction had had an impact. As the review by Professor William Maher put it, “current modelling is not sufficient to understand the effects of these activities”. We hope that more work is put into improving the modelling soon.
Acid sulphate soils occur naturally, and with a natural pattern of droughts and floods, they don’t tend to cause many problems. But this is likely to change in future when climate change makes both long droughts and intense rain events more likely. The problem can also be exacerbated by changes in flow patterns due to river regulation, as has happened in the Murray-Darling Basin at Bottle Bend (near Mildura) and parts of the Edward-Wakool system (near Swan Hill). Prevention of acidity is another example of why we need to return the flows in our rivers to something closer to their natural patterns.
The good news is that the Anglesea River is getting a 24 hour water quality monitoring station, a review of its Estuary Management Plan, a plan for how to manage future incidents and a review of Alcoa’s discharge licence. The other good news is that the Anglesea River’s looking much healthier this year with further outbreaks of acidity unlikely. Which is good for Anglesea locals, the thousands of holiday goers heading down to the Surf Coast over the summer, and the fish.