Khammouane Province occupies an area of 16,315 square kilometres and has a total population of 336,935 people (2005 census). It comprises nine districts - Muang Hinboun, Muang Nakay, Muang Ngommalat, Muang Thakhek, Muang Mahaxai, Muang Boualapha, Muang Nongbok, Muang Sebangfai and Muang Saibouathong. In addition to the majority Lao population, Austro-Thai speakers are represented here by Phu Tai (Tai-Kadai/Tay-Thai/South Western Tay-Thai/Tai) and Seak, Tai Mene, Tai Sam, Tai Yor and Yoi (Tai-Kadai/Tay-Thai/Northern Tay-Thai); and Austro-Asiatic speakers by Bru, Kaleung, Katang, Makong and So (Mon-Khmer/Khmuic) and Krih and Thavung (Mon-Khmer/Viet-Muong). The province contains two vast wilderness areas known as the Khammouane Limestone National Biodiversity Conservation Area and the Nakai-Nam Theun National Biodiversity Conservation Area. The Kahmmouane Limestone National Biodiversity Conservation Area is a maze of limestone karst peaks which form a stone forest of caves, rivers and pristine jungle. For most of the wet season the area is not accessible by road - most 'roads' being tracks (often routes across rice paddies near river banks) with log bridges across deeps streams. During the rainy season, the only way to get around is by boat.