Parks Victoria chief conservation scientist Mark Norman Thursday said the spectacle was the result of green algae at the bottom of the lake at Westgate Park on the outskirts of Melbourne responding to high levels of salt and changing colour.
"The bright pink lake pops up most summers and is made by a native single-celled plant known as Dunalliela that responds to extreme levels of salt in this lake," he said, adding that hot weather makes the salt concentrate further.
"It's completely natural. We often get comments that it looks like an industrial accident of pink paint."
The lake attracts over 140 bird species as well as many curious tourists but authorities warned people to avoid making contact with the pink water, even though it is not dangerous.
"The salt would dry as hard crystals all over your body. It would also be hard on your eyes, like sprinkling salt straight on your eyes," he said.