It had two tributaries: one was the Little Lune arising from the Ered Luin, and the other beginning in the Hills of Evendim north of the later capital of Arnor, Annúminas. It was not connected to Lake Nenuial, the origin of the Baranduin (Brandywine) river.
In the First Age, the course of the river is not known. The Gulf of Lune was not created until the War of Wrath so the river must have had a different lower course. Possibly it connected with the Baranduin further south.