Blue Lake, no colour editing_1

"Mount Gambier's Blue Lake , situated in a volcanic crater, exposes crystal clear water that has filtered underground as it passes slowly under the city through the limestone. Each year in November the lake starts its colour change from winter sombre blue to brilliant turquoise blue, before returning to its winter hue in March.
During winters of high rainfall, surplus water seeps down through the limestone recharging the underground water system.
Making its way gradually to the ocean, the underground water has contributed to the dissolution of the limestone forming many caves beneath the City of Mount Gambier and surrounding areas.
The Blue Lake was formed when the volcano erupted through the limestone allowing the underground water to fill the crater, creating the lake that we see today."
www.mountgambiertourism.com.au/geology.htm