The Sutlej River (alternatively spelled as Satluj River) (ਸਤਲੁਜ, शतद्रु or सुतुद्री, , ستلج, and सतलुज) is the longest of the five rivers that flow through the historic crossroad region of Punjab in northern India and Pakistan. It is located north of the Vindhya Range, south of the Hindu Kush segment of the Himalayas, and east of the Central Sulaiman Range in Pakistan.
Sutlej is sometimes known as the Red River. It is the easternmost tributary of the Indus River. Its source is at Lake Rakshastal in Tibet near Mount Kailas, and it flows generally west and southwest. It waters the ancient and historically important region of Greater Punjab. The region to its south and east is arid, and is known as the Great Indian Desert or Thar Desert.
Sutlej joins with the Beas river in the state of Punjāb, India, and continues southwest into Pakistan to unite with the Chenāb river, forming the Panjnad river south of ancient Multān. The Panjnad joins the Indus river at Mithankot. Indus then flows through a gorge near Sukkur, flows through the fertile plains region of Sindh, and terminates in the Arabian Sea near the port city of Karachi in Pakistan.
The waters of Sutlej are allocated to India under the Indus Waters Treaty between India and Pakistan, and are mostly diverted to irrigation canals in India A huge, multipurpose Bhakra-Nangal Dam has been built on Sutlej by the Indian government. There are several major hydroelectric projects on Sutlej, e.g. the 1000MW Karcham-Wangtoo HEP. A -long heavy freight canal, known as the Sutlej-Yamuna Link (SLY), is also being built in India to connect Sutlej and Yamuna rivers.
The Sutlej was known as or in the Vedic period.
There is substantial geologic evidence to indicate that prior to 1700 BC, Sutlej was an important tributary of the Saraswati river rather than the Indus. Geologists believe that tectonic activity created elevation changes which redirected the flow of Sutlej from the southeast to the southwest. The mighty Saraswati then began to dry up, causing desertification of Cholistan and the eastern part of the modern state of Sindh. The desertification resulted in abandonment of numerous ancient human settlements along the banks of Saraswati.
The source of the Sutlej is just west of Mt. Kailash in western Tibet. This is roadless area, and was first explored by kayak and raft by Russian and German teams in 2004. See First descents of the Sutlej in Tibet.