The Plitvice Lakes lie in a basin of karstic rock, mainly dolomite and limestone, which has given rise to their most distinctive feature. 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. The lakes are divided into the 12 Upper Lakes (Gornja jezera) and the four Lower Lakes (Donja jezera).
The Plitvice Lakes national park is heavily forested, mainly with beech, spruce, and fir trees, and features a mixture of Alpine and Mediterranean vegetation. It has a notably wide variety of plant communities, due to its range of microclimates, differing soils and varying levels of altitude.
The area is also home to an extremely wide variety of animal and bird species. Rare fauna such as the European brown bear, wolf, eagle, owl, lynx, wild cat and capercaillie can be found there, along with many more common species. At least 126 species of birds have been recorded there, of which 70 have been recorded as breeding there.
