Nam Theun (also known as Khading), is a river in Laos, in Khammouane and Bolikhamsai Provinces. Together with its tributaries Nam One, Nam Noy, and Nam Theun it has total length of 138km (86miles) and drains an area of 2800km2. "Nam Theun" is also three options for large dams on the same river, called Nam Theun 1, Nam Theun 1-2 and Nam Theun 2. Nam Theun 2, which was considered the most economic of the three options, is in operation.
Part of the river corridor is a 62,000 hectare national preserve that is one of the protected areas of Laos.