The 3.5-square-kilometre (1.4sqmi) lake lies in the northern part of the Setesdal valley, along the Setesdalsheiane mountains. It has an outlet to the south to the river Otra. The main inlets are Bjålaupet, which enters from Sæsvatn in the north, and Kaldsåi from the west. Together with Sæsvatn, Breidvatn is regulated as a reservoir for the power plants further down the Otra river watershed.[3]