The Khersan River is the largest tributary of Karoon River and originates from the Tang-e- Sorkh Mountains 43 km. southeast of Yasooj and flows under the name of Beshar River towards the northwest of this area.
After passing by the Tang-e-Sorkh Mountains, irrigates several of villages and joins the Tang-e-Sorkh River in the village of Tang-e-Sorkh. Then it enters a valley between the Toop Abdollah Mountains in east and Pazanan in west.
In the mentioned valley, this river passes through many villages. Finally joining rivers by the names of Garmogah and Khersan in the vicinity of Lordegan in Chahar Mahal Va Bakhtiyari. The length of the Khersan River is 230 km. Suitable recreational areas can be found throughout the course of this river.