Rock pool at popular Sydney beach turns green

A mysterious fluorescent green liquid has been pouring into a rock pool at a popular Sydney beach, with locals vowing not to swim.

A mysterious fluorescent green liquid has been spotted pouring into a public ocean-water rock pool at a popular Sydney beach, with locals vowing not to swim until it disappears.

The liquid is believed to be a natural fluorescent dye, fluorescein, and was seen gushing into the usually clear waters of Cronulla on Friday.

The dye, which was spotted pouring out of a pipe and into a rock pool at the southern Sydney beach, is often used to help experts track the flow of water and identify leaks in a water system.

Mysterious green liquid has been seen pouring into a Sydney rock pool. Picture: Facebook.

Many locals declared that they would not swim until the chemical dissipated, which should take between five to seven days as it naturally degrades through exposure to sunlight.

“We believe the discolouration is likely to be fluorescein dye, which is commonly used in plumbing/drain testing and dissipates quickly once diluted,” a spokesperson for the New South Wales Environmental Protection Authority said.

The dye has low toxicity, but the authority said it should be used minimally as “even small amounts can be highly visual”.

The liquid, which was seen at Cronulla, was identified as fluorescein. Picture: Facebook.

Australian dye manufacturer Tintex describes fluorescein as a “water colourant used to locate leaks in plumbing, tracing pipe locations, detect drain damage and water pathways”.

“It is non-toxic to the environment and odourless,” Tintex wrote about the dye, which retails for $21.95 per 100g.

“Available in Bright Blue, Bright Green, Bright Red, Bright Yellow and … Fluorescent Green.”

In a safety data sheet, the company warns: “Do not let this chemical enter the environment.”

Potential health effects include eye irritation, skin irritation, irritation of the digestive tract and respiratory tract irritation.

The New South Wales Environmental Protection Authority confirmed the dye was non-toxic, though local manufacturer Tintex recommends that it isn’t released into the environment. Picture: Tintex.

Social media users helpfully pointed out that the dye was mostly “harmless” after photos of Cronulla’s bright green rock pools were posted to a locals’ Facebook page.

One user claimed the dye was “legal to use in a stormwater drain”.

“Doesn’t look good whatever it is,” another responded, while other cautious residents said they wouldn’t swim in the area until the dye dissipated.

Visitors to the Melbourne CBD were similarly perplexed on Thursday when a section of the Yarra River was dyed by the same chemical.

A photo was posted to Reddit of a section of the river, just below Flinders St Station, with the caption: “What is this from under Flinders?”

The dye similarly perplexed Melburnians when it flowed into the Yarra last Thursday. Picture: Reddit.

By Thursday evening, the discolouration had dissipated and Melbourne Water confirmed it had come from the Elizabeth St main drain, which is adjacent to Flinders St Station.

“Our operations personnel immediately conducted safety inspections alongside EPA (Environment Protection Authority) Victoria across the affected area as a precautionary measure,” a spokesperson said.

“We can confirm, there is no impact to the health of our waterways following further safety inspections this morning,” they added.

🟢 Not your regular #Venice gondola ride!

🛶 The waters in #Venice's main canal turned fluorescent green on Sunday.

🚨 The Venice prefect has called an emergency meeting to understand what happened and study possible countermeasures

📸 Vigili del Fuoco via REUTERS pic.twitter.com/qyANTlkoFA

— FRANCE 24 English (@France24_en) May 29, 2023

Just over a week prior, locals and tourists in Venice, Italy were left scratching their heads as one of the city’s famed canals also glowed bright green.

The Regional Agency for Environmental Prevention and Protection of Veneto, a region of Italy that encompasses Venice, said fluorescein had shown up in samples taken.

The agency also confirmed the results of their analysis had “not shown the presence of toxic elements”.