Zorkul (or Sir-i-kol) is a lake in the Pamir Mountains that runs along the border between Afghanistan and Tajikistan. It extends east to west for about 25 km. The Afghan-Tajik border runs along the lake from east to west, turning south towards Concord Peak (5,469 m), about 15 km south of the lake. The lake's northern half lies in Tajikistan where it is protected as part of the Zorkul Nature Reserve. Out of the lake, towards the west, flows the Pamir River, tracing the Afghan-Tajik border. It is therefore a source of the Amu Darya or Oxus River.