This spectacular expanse of open grassland covers 320 sq. km in the south-west corner of Kenya. It receives ample water from the tree-lined Mara River, a tributary of the Talek River. The western border of the park features the Oloololo Escarpment as well as the highest concentration of game. This area is often difficult to traverse as the swampy ground often becomes impassable after heavy rains. Because of its accessibility from Nairobi, the eastern edge of the park is most popular with tourists and minibuses. The highlight of the Mara is undoubtedly the great migration of wildebeest which move north from the Serengeti in July and August in search of lush grass. They return south in October before the rainy season. Watching millions of these animals move together in mass is truly a humbling experience for human visitors. The official designation of the Maasai Mara is as a park reserve, and it therefore does not have national park status. The primary difference is that a park reserve allows people to graze their animals and shoot game if they are attacked.