Slovenia has some of the greatest subterranean biodiversity in the world. The aquatic fauna, with its 200 species, is by far the richest, while the terrestrial fauna, with 150 species, is second only to the more southern areas of the Dinaric karst. Five Slovenian cave systems have been listed among the 20 richest cave systems in the world. The Postojna-Planina Cave System, with its 50 aquatic and 35 terrestrial species is by far the most abundant. The Cave Protection Act protects the subterranean environment as a whole.