The river Osum is 161 km long from its source (in the Vithkuq mountains, close to the border with Greece) to the town of Ura Vajgurore, where it joins the Devoll River, to create the Seman River. The stream of the river can be divided in three parts, the upper stream, the middle stream and the lower stream. The upper and middle stream cross through a mountainous and hilly area, and will be used for the construction of the power plants. The water basin that feeds the Osum River is bordered in the north with the Devoll River, in the south with the Vjosa River and in the east with the Greek border. The river has a water catchment area of 2142 km2.