LIS:
I just assumed you already know this lake since youre from Australia.
Jason:
Since "I dont know" probably isnt the answer youre looking for, I googled it for you lol
"The reason for the lake's color is still under investigation, and so far no one has come up with a reasonable explanation. However, the most probable explanation according to some scientists involves the low nutrient concentrations and growth of Dunaliella salina & Halobacterium."