The Plitvice Lakes complex was declared a national park on April 8, 1949. It is the largest, oldest and most visited Croatian national park. It is a wooded mountain area with 16 lakes of different sizes, which descending from 636 to 503 meters altitude, filled with crystal blue-green water. The lakes get their water from numerous rivers and streams, and are interconnected by cascades and waterfalls. Travertine barriers, which were formed over a period of ten thousand years, are one of the fundamental features of the Park. The special geographical position and specific climatic features have contributed to the emergence of many natural phenomena and rich biodiversity. Travertine sediments have been formed from the Pleistocene to the present day in sinkholes and depressions between the surrounding mountains. The Upper Lakes in the south are predominantly composed of dolomite, and the Lower Lakes in the north of limestone rocks. Spacious forest complexes, exceptional natural beauties of lakes and waterfalls, richness of flora and fauna, mountain air, contrasts of autumn colors, forest paths and wooden bridges and much more are part of a unique whole that was declared a UNESCO World Natural Heritage Site in 1979. the first in the world. The park is divided into a narrower and a wider zone according to the degree of protection. The source of the river Korana, which is fed by water from the lake, is also located on Plitvice Lakes. The climate in the national park is temperate mountainous. The first serious beginnings of tourism in Plitvice Lakes date back to 1861. In 2011, there were more than a million visitors for the first time in the history of this national park.