river in western Afghanistan, rising on the southern slopes of the Band-e Bāyan Range, flowing southwest past the town of Farāh, and emptying into the Helmand (Sīstān) swamps on the Iranian border after a course of 350 miles (560 km). The river fluctuates greatly with the seasons, sometimes flooding in the spring and becoming impassable. Its waters are used for irrigation along much of its length.