Ewaso Nyiro River

Major Rivers in Isiolo

The Mighty and Invaluable Ewaso Nyiro River

The drainage pattern Isiolo County is dominated by the Ewaso Nyiro River, which often flows when all other rivers are dry thanks to high rainfall at its headwaters in Mount Kenya and Aberdare Ranges. It has reached the stage of early maturity, for although flowing quickly, its course meanders via a wide belt of its own alluvium. When tributary streams reach the alluvium they often flow along its edge instead of cutting directly to the main river. The flow of Ewaso Nyiro River diminishes east of Merti Plateau, owing of evaporation, before terminating in the Lorian Swamp.

All rivers flowing within Isiolo County, excepting the Tana, are a part of the Ewaso Nyiro drainage pattern. River Tana flows in the southern area demarcating its short boundary with Tana River County. Rising from the western slopes of Mount Kenya, the mighty Ewaso Nyiro, traversing seven semi-arid counties on its 700 km course to the Lorian, is the major lifeline for the people, livestock, and the swag wildlife. It dissects Isiolo County into two: To the north of the river is the Merti Plateau and to its south are the wildlife rich plains lying at an altitude of 1,000 ms asl. Further north, River Ewaso Nyiro is crossed nearby Archer’s Post.


Kenya is blessed with several rivers, each playing a vital role in the country’s ecosystem, economy, and culture. The longest of these is the Tana, stretching approximately 1,000 kilometers from its source in the Aberdare Mountains to the Indian Ocean. Long, wide, short, seasonal, the rivers that crisscross Kenya each contributes to the natural beauty, biodiversity, and socio-economic success.


Isiolo County, with its strategic location, rich cultural heritage, and potential for development, is a unique region in Kenya. It features a mix of semi-arid and arid landscapes, with some areas of savannah and bushland, and home to several wildlife reserves and conservancies, including the Buffalo Springs National Reserve, Shaba National Reserve and the famed Lewa Wildlife Conservancy.

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What’s The Air Like In Isiolo?

Isiolo is almost always hot and dry at most months of year, with a mean of 30oC, and two rainy seasons. The rainfall received is historically erratic, scarce and unreliable.

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