It is located in Kajiado County. It has 39,206 hectares at the center of an 8,000 square kilometer ecosystem, which spans across the international border between Kenya and Tanzania. The local people are mainly Maasai, but people from other parts of the country have settled there, attracted by the economically driven tourist success and intensive agriculture along the swamp system that make this low-rainfall area one of the best wildlife viewing experiences in the world, with 400 species of birds, including waterfowl, pelicans, and 47 types of birds of prey. In 1991 it was declared a biosphere reserve.