The river name, Ngounié, is a French rewording of "Ngugni", which was originally used by Vili language speakers in the Samba Falls/Imperatrice Falls area in the mid-1800s to call the northern border of their district, "Nsina-Ngugni".

[1] When Robert Bruce Napoleon Walker and Paul Du Chaillu arrived in the area, they wrote down "Ngouyai" or "Ngunyé".

The first part of these names means "body of water" in the given languages, and "manga" refers to dwarf palm trees which grow along its bank.

For 60 kilometres (37 mi), the river has a south and then west flow, and forms a border with Congo.

It then establishes a floodplain within a 220 kilometres (140 mi) valley between the Moukande Mountains[dubious – discuss] and the Massif due Chaillu.

[2] The Ngounié River Valley is formed between the forest-covered Du Chaillu Hills and the Ikoundou Mountains, and has grassy vegetation.

[5] The hydro-power potential of the Ngounié River has been proposed to be tapped by a hydroelectric project located on the Empress Eugénie Falls.