https://en.wikipedia.org/wiki/Mamberamo_River

The river's huge valley is home to various uncontacted peoples and incredible biodiversity. In the 1990s, the Indonesian Government had plans to construct a large hydroelectric dam on the Mamberamo that would have submerged much of the area. This plan was shelved after the Indonesian financial crisis from 1998 to 1999, but there are concerns by environmental groups that it could be resurrected sometime in the future. At present, the Mamberamo remains the second largest river in the world to be completely unfragmented by dams in its catchment, behind only the relatively nearby Fly.