Kelimutu is a volcano, close to the small town of Moni in central Flores island in Indonesia. The volcano is around 50 km to the east of Ende, Indonesia, the capital of Ende regency in East Nusa Tenggara province. The mountain has three volcanic crater lakes that differ in color.
The science of the Kelimutu lakes is relatively well-known.
Lake colors periodically change due to adjustments in the oxidation-reduction status of the fluid of each lake, and also considering the abundance of different major elements, such as iron and manganese.
Oxidation-reduction status depends on the balance of volcanic gas input and rainfall rate, and is thought to be mediated by the groundwater system in the volcano itself. The colors in the lakes change independently from each other, as each has its own unique connectivity to the underlying volcano's activity.
Between January and November 2016, the colors of the craters changed six times. Although it is widely believed that the changes are unpredictable, it is more accurate to say that the lack of any regular monitoring of the volcanic system precludes scientists from having the data necessary to drive widely available predictive models.
According to en.wikipedia