Ruaha National Park takes its name from the Ruaha River, which flows along its southeastern border. The river provides permanent water in the park, and during the dry season animal concentration along its banks is spectacular. Ruaha National Park is about two to three hours drive from Iringa, a famous town on the Dar es Salaam to Zambia highway. Covering an area of 20,226 square kilometers, Ruaha is the largest National Park in Tanzania. Its borders were extended in 2008 to include Usangu Game Reserve to protect the Ihefu wetlands and the Great Ruaha River catchment areas and biodiversity. This unspoilt wilderness is rich in flora and fauna, and contains a wide variety of animals that includes Greater and Lesser Kudu, roan and sable antelopes, which are rarely seen in most other game parks especially in Northern Tanzania. Ruaha National Park is famous for its herds of elephant and buffaloes. The Ruaha River, which plays an important role in the ecosystem of the park, provides sanctuary to a large number of hippos and crocodiles. During the dry season the river attracts great quantities of game including lions, leopard, hunting or wild dog, impala, waterbuck, warthog, giraffe, and elands. In the plains ostriches, cheetahs and Grants Gazelles can be seen. The park is rich in bird life throughout the year, with over 450 bird species recorded. The best time for game viewing is during the dry season, from May to December. During the wet months from January to April some tracks become impassable.