The Plitvice Lakes represent a series of tufa lakes and waterfalls. The evolution of this ensemble is closely related to karst phenomena: lakes are dammed by barriers of travertine, such as shown in this photo, which formed due to the precipitation of calcite from the water. The area was declared a national park in 1949 and a UNESCO World Heritage Site in 1979. It is equipped with a system of walkways and has become a scene of mass tourism.