It rises in the Izera Mountains, part of the Western Sudetes range, where it runs along the border with the Czech Republic. At the slope of the Smrk massif it turns northwards, flowing along the towns of Świeradów-Zdrój, Mirsk, Gryfów Śląski, Leśna, where it is dammed at the Lake Leśnia reservoir, to Lubań, Nowogrodziec and Kliczków. It finally joins the Bóbr river approximately north-west of Małomice and south-east of Żagań. For most of its length it is in Lower Silesian Voivodeship, but it also flows through Lubusz Voivodeship for several kilometres before reaching its mouth.