Ruaha National Park is Tanzania's largest, a vast wilderness in the south-west of the country visited by only a handful of travellers each year. At the park's heart is the aptly-named Great Ruaha River, a massive watercourse that dwindles to only a few pools in the dry season, but bursts its banks and roars over boulders at the height of the rains. Converging with the Great Ruaha are hundreds of sand rivers, natural game corridors when dry and sparklingly clear streams when wet. Waterbuck, impala and the world's most southerly Grant's gazelle risk their lives for a sip of water - the shores of the Ruaha are a permanent hunting ground for lion, leopard, cheetah, jackal, hyena and the rare and endangered African wild dog. Ruaha's elephants are recovering strongly from ivory poaching in the 1980's and remain the largest population in East Africa. Ruaha represents a transition zone where eastern and southern species of flora and fauna overlap - lesser and greater kudu co-exist with northern species such as Grant's gazelle.