Adam Marshall Media Statement: Lake Wyangan Fish Death
On 23 and 24 May 2020 a significant fish death occurred within Lake Wyangan, affecting hundreds of thousands of fish.
Lake Wyangan, which sits within the Griffith LGA and receives water from the Murrumbidgee Irrigation Ltd (MIL) network, is not a natural waterway, however is regularly stocked with fish by NSW Department of Primary Industries (DPI) Fisheries for the purpose of recreational fishing.
DPI Fisheries received reports of the fish death event on 24 May 2020 and staff attended the scene the following day, confirming the initial reports of the magnitude of the fish deaths. An investigation into the likely cause of the event was led by the NSW Environment Protection Authority (EPA) in collaboration with DPI Fisheries.
The investigation included analysis of water quality samples and tissue samples from affected fish. Analysis of water samples ruled out localised pollution or pesticide as a cause of the fish deaths. This finding was supported by an independent analysis of water quality data commissioned by NSW DPI Fisheries.
This analysis found that while there is insufficient evidence to determine a single, specific cause, hypoxia was involved with the fish deaths and there is a strong possibility that the cause of the event was the disturbance of sulfidic sediments by inflows into the lake prior to the fish deaths.
There were two significant inflows into Lake Wyangan North prior to the fish deaths. The first was an inflow of several hundred ML of storm water (peak flow of about 40 ML/day) from about 29 April until about 4 May. The second was a 242 ML "fill" of irrigation water which entered the lake over about a 6-day period starting on around 5 May.
Both reports provide a series of recommendations for future monitoring, mitigation and management of the Lake to prevent similar events in the future.
A copy of the report is available here https://www.dpi.nsw.gov.au/fishing/habitat/threats/fish-kills
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