The Ndji river is 238 kilometres (148 mi) long.

It rises to the east of the Pata sandstone plateau and skirts the eastern escarpment before crossing it.

[1] The Belgian explorer Léon Hanolet travelled up the valley of the Bali (Mbali) river and the upper Kotto River in 1894, following the road of the Arab caravans.

He described the country as flat, and sometimes walked for six hours without crossing a stream.

[3] The river is home to the Syncerus caffer aequinoctialis subspecies of the African buffalo.