Why part of the Yarra River in Melbourne under Flinders St Station turned fluorescent green

Some residents and visitors to Melbourne’s CBD have pondered what led to a stretch of the Yarra River turning fluorescent green.

A photo of a stretch of river just below Flinders St Station with a green tint that looked like it had been dyed was posted to Reddit on Thursday.

The photo captioned, “What’s that from under Flinders?”

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Most replies joked that it could be “dropped broken lightsticks” or a delayed St. Patrick’s Day celebration, but some suggested it could be an algal bloom or a leak in a building.

As of Thursday evening, the discoloration had disappeared and Melbourne Water confirmed it came from the main outlet on Elizabeth St, which is adjacent to Flinders St station.

“As a precautionary measure, our operations staff, in conjunction with the EPA (Environment Protection Authority) Victoria, immediately conducted safety inspections throughout the affected area,” a spokesman said.

Melbourne Water said the discoloration was caused by fluorescein, a non-toxic drain dye commonly used by plumbers to check connections to underground pipes.

“We can confirm that following further safety inspections this morning there is no impact on the health of our waterways,” the spokesman said.

EPA officials also examined the discoloration and concluded that it appeared to be fluorescein.

Although it has mostly dissipated, the EPA advised the public to avoid contact with this or any future leak until it can be confirmed what it is.

In 2017, a similar incident happened where the same part of the Yarra turned bright green from fluorescein, which eventually dissipated.