Ammon News - The colouring was spotted in Careening Cove at Milson Park, Kirribilli, near the city’s central business district and home to one of the prime minister’s official residences.

One local told 9News the water resembled “green cordial” and the “radioactive stuff you see in superhero movies”. However Supt Adam Dewberry from Fire and Rescue NSW said there was no indication the substance was toxic and it is most likely a fluorescein dye.

He compared the unplanned occurrence to the annual St Patrick’s Day event in Chicago, during which the river is temporarily dyed green.

The dye had come out of a storm water drain in Kirribilli – an old suburb at the bottom of a large hill – so Dewberry said there are “thousands of areas where it could have entered”.

“So it’s unlikely we’ll be able to identify the source, where it did come from, because there’s just so many access points into the storm water … in that area,” he said.

Dewberry said FRNSW had spoken with Sydney Water, which said it had not used the dye in the area.

There are a number of theories as to what caused the fluorescein spill, including a potential year 12 “muck-up day” prank. Prof Khan said this was “plausible”, though could also be a result of “misuse or poor practice for its intended purpose”.

He said the rain might also be a potential factor.

“It might have been sitting there in a storm water system for a couple of weeks or something, and it might just be the fact that it started raining that’s washed it out,” he said.

The Guardian