There have been a couple of questions baffling the public about the lake under the Westgate Bridge. 

The first one is how the heck did it completely change colour?

The second, much like the ‘gold or blue dress’ fiasco a couple of years ago, is whether it’s purple or pink.

While we may never settle the second, it looks like we’ve found an answer to the first. 

Biologist Peter Beech told 9News it’s because the hot weather causes a green algae to mix with a purplish bacteria.


This then reacts with the salt crust at the water bed creating the pink water. 

“There’s a couple of organisms in the water that causes the pink pigmentation,” he said.

“One of them – weirdly – is a green alga that contains beta carotene, which colours carrots and is really good for us.”

It’s ended up being a tourism sensation, with international tourists making sure to make it one of their Melbourne pit stops. 

If you want to catch in person, head down there this weekend, as the cooler weather means it might only last another week or so.