[3] It originates in the central east-west mountain range of New Guinea and flows southwards into the Arafura Sea at Flamingo Bay.

During the first two Dutch expeditions to Southern New Guinea (1907–10) it was called Northern River.

After it became part of Indonesia, it was renamed to Unir, as in the language of the local Asmat people, while the Lorentz name is still in use.

Three large Dutch expeditions led from the mouth upstream to the central snow-capped mountains, which were still unexplored.

The warmest month is October when the average temperature is around 23 °C, and the coldest is July, at 20 °C.