Fears of mass fish deaths in Anglesea River

FEARS of another mass fish kill in the Anglesea River have led authorities to develop a plan to pump stored water into the estuary, artificially open the river mouth so fish can swim out to sea, and manually relocate those that remain.

A rare month-long natural opening of the mouth has allowed fish back into the river system for the first significant length of time in three years, but sand has returned and the Corangamite Catchment Management Authority (CCMA) believes its now closed to the sea.

“This is likely to result in increasing acidity over the coming weeks, especially if rainfall mobilises acid sulphate soils in the upper catchment wetlands,” Corangamite CMA chief executive officer John Riddiford said.

Combined with a drop in river levels, the CCMA is worried acid sulphate soils at the upstream Coogoorah Park will be activated and release metals and acids into the river system, a leading cause of at least six kills in the past 20 years.

Mr Riddiford said the stored water to be released was already highly acidic, but “the risk of continued low water levels in the estuary activating additional areas of acid sulphate soils has been identified as a more significant and irreversible overall risk”.

The CCMA-led plan has been devised in conjunction with the Department of Energy, Environment and Climate Action (DEECA), Barwon Water, Surf Coast Shire, Great Ocean Road Coast and Parks Authority, EPA and Wadawurrung Traditional Owners Aboriginal Corporation.

The authorities’ plan to dig out the river mouth if water quality reaches “a trigger point which is harmful for fish”, allowing fish access to the ocean.

“DEECA and Corangamite CMA may also co-ordinate manual fish rescue to remove the fish,” Mr Riddiford said.

Friends of Anglesea River member Dick O’Hanlon said the plan was aimed at “avoiding an unsightly and embarrassing fish kill.”

While agreeing the need to prevent excessive drying of the system was “critical”, he said the proposed actions do nothing to reduce the chronic acidity in the estuary.
“Rather than rush into using the highly acidic stored water, perhaps we should quickly review the pros and cons of managing the berm level to ensure at least intermittent connection with the sea.”

Mr O’Hanlon and FOAR have long held the belief that the cause of acidity in the system is likely linked to the 50-year drawn down of an aquifer beneath the area by Alcoa, that’s in turn dropped the water table and exposed naturally acidic soils.

Alcoa, DEECA, and local water regular Southern Rural Water maintain there’s “no evidence of adverse impacts on groundwater dependent ecosystems, including the Anglesea River.”