The Ewaso Ngiro, also known by the name of Ewaso Ng'iro or Ewaso Nyiro, is the Kenya river born on the Western slopes of Mount Kenya and on the Aberdare range, in the central plateau, and flows first North, then to the East and finally South-East to head towards Somalia where it enters the Jubba River.
The upper basin of the Ewaso Ngiro, the largest of the five reservoirs of Kenya, covers an area of 15,200 sq km; it is a permanent river that is fed not only by seasonal rains, but also by the glaciers of Mount Kenya.
The river is a key element for the survival of many species of wild animals, but it also supports economic development and population growth of the people living along its course; on its way through the arid and semi-arid lands of seven districts: Meru, Laikipia, Samburu, Isiolo, Wajir, Garissa and Marsabit.
Ewaso Ngiro in local communities language means "brown river" or "muddy river."
In the arid Northern Kenya water means life and the waters of this river guarantee the survival of wild animals that are found in the Samburu National Reserve, in the Shaba National Reserve and in the Buffalo Springs National Reserve.
Further downstream the river pours its waters into the Lorian Swamp, a vast marshy area.
The river also supports the agricultural development that took place along its banks, providing a reliable source of water for the irrigation of crops.
One of the tributaries of the Ewaso Ngiro is the Ewaso Narok that, near Nyahururu, gives life to the Thomson Falls that are 72 meters high and were discovered in 1883 by Joseph Thomson.