Water samples taken at Manly Lagoon in Queenscliff a fortnight ago have shown no evidence to explain the death of an unusual number of dead fish detected along the waterway a fortnight ago.
Fisherman Kyle Larsen noticed a suspicious number of fish carcasses starting at Pittwater Road Bridge down toward the opening of the lagoon on Bridge Road in Queenscliff on Tuesday, 25 July.
He reported the incident to the Environmental Protection Agency (EPA) and Northern Beaches Council, and alerted Manly Observer to what he saw as a potential poisoning issue. Kyle said he would hate to see a repeat of the mass fish kill that affected the area almost 20 years ago after pesticides were washed the stormwater drains, leading to 10,000 dead fish and bird life.
Our investigations with the EPA led us back to Council, who confirmed that Council staff “visited Hinkler Park on Tuesday evening and identified approximately 10 dead fish in the water.”
However, Council advised that it appeared to be an isolated incident with no apparent cause and no visible signs of pollution. When Council staff returned again on Wednesday there were no further impacts observed, and fish were seen swimming in the area, they said.
When a Manly Observer representative visited on Thursday and observed several more dead fish toward Bridge Road we were advised these were likely the same dead fish as they had not been removed. We were however told that Council officers would return to the site today (Friday, 28 July) to take water samples, and results will be reported back in one week.
The EPA confirmed they will assist Council with inquiries as needed.
Council advised us today, 7 August 2023, that “Laboratory results have concluded no significant contamination by foreign substances commonly associated with pollution events.
No additional mortalities have been observed and aquatic fauna, fish and birds, are behaving normally in the lagoon.
Council encourages the community to report any suspicious activity that may impact on the health of our waterways as soon as possible so it can be investigated.”
A collection of dead fish in our waterways does not necessarily mean a poisoning or atypical pollution event has occurred. Sometimes a change in weather (heat or surge of rain) can affect the level of available ‘dissolved’ oxygen which fish need to survive. On the Monday night before the dead fish appeared the Manly area received 22mm on Monday, Bureau of Meteorology data shows.
A council document on the topic references the impact of adverse weather events, as well as algae buildup as a factor in fish kills because of this lack of dissolved oxygen. However, it says there are also “many things that need to be considered including the possible presence of pesticides, toxins and diseases. You can help by contacting Council on 1300 434 434 if you see any suspicious behaviour or pollution in our bushland, creeks, drains or lagoons.”
“You can also make a difference by washing your car on the grass, limiting the amount of fertiliser and pesticide you use in the garden and making sure that grass clippings do not enter stormwater drains.”
You can also report a concern over pollution to Council via this link.