The Selous Game Reserve, is the largest well-watered wildlife sanctuary in Africa, and one of the largest protected areas in the world. Its size is simply stunning, bigger than Switzerland, uninhabited and little touched by human interference. It is perhaps one of the most pristine wildernesses still remaining in Africa, with a wide variety of wildlife habitats, including open grasslands, Acacia and miombo woodlands, swamps and riverine forests in the many tributaries of the mighty Rufiji River which flows through the reserve. Due to its unique ecological importance, it was designated a World Heritage Site by the United Nations in 1982. Its wildlife is spectacular, with some of its mammal and reptile populations the largest in Africa, namely buffaloes, elephants, hippos, wild dogs and crocodiles. Most of the reserve remains set aside for game hunting through a number of privately leased hunting concessions, but a section of the northern park along the Rufiji River has been designated a photographic zone and is a popular tourist destination. Interesting places in the park include the Rufiji River, which flows into the Indian Ocean opposite Mafia Island and the Stiegler Gorge, a canyon about 62 feet (100 m) deep and 62 feet (100 m) wide. Walking safaris are permitted in Selous Game Reserve, and boat safaris on the Rufiji River are a popular activity.