The river rises from a natural spring to the North West of the Ngong Hills at a settlement called Kerarapon.
The river is somewhat fortunate, in that it does not run through a built up area, until it reaches the sprawling conurbation in North Kajiado called Ongata Rongai (meaning Narrow Plain in KiMaa language).
All along its northern boundary it is somewhat protected by middle class homes and as it flows east and abuts the Nairobi National Park.
It then benefits from environmental protection by extension of the National Park and by reduced interference on its northern and to some extent, its southern bank too.
Several key streams, particularly the Mokoyeti and Sosian, which rise in the Ngong Road Forest, feed the river via the National Park.