Besides climate change, upstream dam building presents potentially large environmental problems. Studies indicate that if all planned mainstream Mekong dams are built, the lower Mekong will be converted into a series of reservoirs. In China, where the Mekong is known as the Lancang, this has already happened. Four dams have been built, turning the river into a succession of large lakes. If the Mekong dams are not engineered to deal with sediment flows, fish migration and coordination of water release, there is potential for strong impacts downstream.