valley of Tjentište. Rivers and lakes Rivers The Piva and Drina rivers are the largest rivers in the park, and they form its north-western border. The Sutjeska River could be considered the main river basin largely located within the park itself. The Sutjeska divides Zelengora Mountain from Maglić, Volujak and Bioč mountains, and has carved an impressive canyon deep, and Tjentište valley through the middle of the park. Other rivers are all tributaries of the Sutjeska. Left tributaries are Klobučarica Creek, Jabučnica Creek, and Hrčavka River. Right tributaries are Suški Creek (also called Suha River or Creek Sušica), Prijevor Creek, and Perućica Creek. Lakes The Zelengora mountain hide in its forests and wide and grassy plateaus, 9 glacial lakes, also known as "Gorske oči" (literally translated in Eng.= "Eyes of the Mountain"). These lakes are: Crno Lake, Bijelo Lake, Orlovačko Lake, Gornje Bare Lake, Donje Bare Lake, Štirinsko Lake, Kotlaničko Lake, Kladopoljsko Lake, and Jugovo Lake (also called Borilovačko Lake). Climate The park's climatic condition is a transitory zone. Moderate continental climate dominates from the north while the influence of a southern Mediterranean climate is less pronounced. The typical mountain climate is also largely moderated by the Adriatic Sea. Flora The park's vegetation comprises thick forests (66%) mountain pastures, meadows and rocky ground above the forests. In particular, the northwestern hill slopes have thick coniferous and beech trees up to an elevation of , while in the other directions, the hill slopes are very steep, barren and rocky. Pastures are found at elevations above in the plateaus. Its floral wealth comprises 2,600 species of vascular plants (many of them rare and endemic) and also about 100 species of edible fungi. Perućica forest consists of large beech trees as high as or more, with girth of about , and endemic black pines which stem from the rocky faces that provides protection to the ancient forest in the entire valley. The trees in the Perućica primeval forest have never been logged and some of them are as old as 300 years. Fauna The animal population is diverse and considerable. Bear, chamois, boar, wolf, pine marten and mink marten, wild cat, fox, and wild goats have been sighted in the park, particularly in the Perućica forests. The park has more than 300 species of birds in the large areas of lakes (nine lakes on the Zelengora mountain range in the park) and wetlands.