These lakes are named Tiwu Nuwa Muri Koo Fai, Tiwu Ata Polo, and Tiwu Ata Mbupu by the local people of the Kelimutu area (named left to right). Translated to English, these lakes are called the Lake of Young Men and Maidens, Enchanted Lake, and Lake of Old People (English translations, left to right). These crater-formed bodies of water have deep roots in Indonesian history. Indigenous peoples believe that the lakes are the resting places of their ancestors, and the varying colors of the lakes are due to changing moods of these spirits.
The scientific explanation, however, is that these lakes are, in fact, summit lakes of a volcano. Fumaroles (openings in the earth's crust present in volcanic terrain) beneath the surfaces of the lakes emit volcanic gases like sulfur dioxide. This volcanic activity, in turns, alters the location of aqueous minerals (primarily salts and oxides). Denser, mineral-rich water near the bottom of the lakes is forced upwards. This displacement in the close yet isolated lakes causes the visible color changes in the lake.
Geological surveys of the lakes commenced after the death of a tourist falling down the lake's steep cliff's into the water in 1995. The results yielded startling measurements - water temperature of 37 degrees Celsius (98.6 degrees Fahrenheit) and a pH of 0.5, highly acidic. Bubbles are often reported to be seen on the lakes' surfaces, due to the volcanic and seismic activities of the proximate volcano and phreatic eruptions of magma.
Image credit: Photo Vide, http://photovide.com/
Navarra, John Gabriel. Contemporary Physical Geography. Philadelphia: Saunders College Pub., 1981, 94