By Tanya Steele
Ferntree Gully Quarry Reserve Lake has had ongoing water fluctuations since last year, with recent weekly testing showing water to still be unsafe for swimming or ingesting any fish caught at the popular recreation site.
Water safety levels last year in late November resulted in signs being erected at the reserve by Knox Council after routine testing detected E. coli bacteria.
“The last testing was done on 10 February 2025, which categorised the water quality within Quarry Lake as not suitable for swimming and not to be ingested.” the Knox Council website page read.
E. coli is a bacterium commonly found in the gut of humans and warm-blooded animals and its presence indicates faecal contamination from sources such as stormwater runoff, sewage, dog poo, or wildlife waste.
Most types of E. coli are not considered harmful to humans and animals. However, the presence of these bacteria in the water may indicate other disease-causing bacteria, viruses, and protozoa which can make swimmers or people who eat fish from the water sick.
A representative from the Council said there are various sources of contamination that impact lakes such as the one at Quarry Reserve.
“Water sampling, testing within a nationally-accredited laboratory and reporting are undertaken by a suitably qualified consultant on Council’s behalf,” they said.
“Being static, lakes are more prone to spikes in bacteria, nutrients, algae and pathogens as there’s no opportunity for things to be ‘flushed’ through the system.”
The council tests for bacteria, blue-green algae, dissolved oxygen and other water health indicators and a Victorian Fisheries Authority spokesperson said the VFA is aware of high blue-green algae levels at Quarry Lake.
“While people can still go fishing, we recommend you avoid contact with the water where possible and don’t eat the fish you catch.”
“We don’t believe the algae levels pose a significant risk to the health of the fish.”
The VFA regularly stocks it with catchable rainbow trout as well as Australian bass and Murray cod fingerlings to create year-round fishing opportunities.
Before any fish are stocked, VFA staff from their organisation hatcheries test water quality with specialised equipment to ensure the fish are entering suitable conditions.
A TikTok influencer named Siri|Melbourne Hotspots recently mentioned the spot in early February as a hidden oasis in Melbourne’s east and the perfect spot for a picnic by the water in their things to do series online.
“Just a quick PSA, the water here usually isn’t great for swimming,” the post said.
“The views are so stunning,…Whether you’re here for a family outing or for some quiet time, it’s a stunning little gem to explore.” Siri said.
The quarry area was given a facelift in early 2023 when upgrades were funded through $1.7 million from the government, $600,000 from Knox City Council and $50,000 from the Victorian Fisheries Authority (VFA).
Visitors can reduce the risk of contamination by cleaning up after their dogs and putting their rubbish in bins.
If you have experienced any symptoms including diarrhoea, abdominal pain, cramps, fever, respiratory infections, ear infections, or skin rashes after swimming in or eating fish from the lake, please seek medical attention.
Knox Council continue to provide up-to-date information for the community monitoring the water quality from October to March to ensure the space is safe to visit.
More information and updates may be found on this Knox council website page:
https://www.knox.vic.gov.au/our-services/gardens-environment-and-sustainability/quarry-lake-water-quality
