The Plitvice Lakes is a national park in Croatia in the Plitvice Lakes municipality, in the mountainous region of Lika.
The national Park is underlain by karstic rock, mainly dolomite and limestone with associated lakes and caves, this has given rise to the most distinctive feature of the lakes.
The lakes are separated by natural dams of travertine, which is deposited by the action of moss, algae, and bacteria. The encrusted plants and bacteria accumulate on top of each other, forming travertine barriers which grow at the rate of about 1 cm per year. The lakes are renowned for their distinctive colours, ranging from azure to green, grey or blue. The colours change constantly depending on the quantity of minerals or organisms in the water and the angle of sunlight.