Plitvice Lakes National Park is one of the oldest and largest national parks in Croatia. In 1979, Plitvice Lakes National Park was inscribed on the UNESCO World Heritage list, due to its outstanding and picturesque series of tufa lakes, caves, connected by waterfalls. Sixteen lakes can be seen from the surface. They are separated by natural dams of travertine, which is deposited by the action of moss, algae, and bacteria. The lakes are renowned for their distinctive colors, ranging from azure to green, grey or blue. The colors change constantly depending on the quantity of minerals or organisms in the water and the angle of sunlight. Source: https://en.wikipedia.org/wiki/Plitvice_Lakes_National_Park