In Laos / Cambodia, it is 95% China to blame. Well, technically, it is Laos/Cambodia for selling out their country to China. China is building a silk road all the way to Sihanoukville. Google it, there are a ton of problems. I've seen them first hand. Total destruction of the land to build railways and roads, with zero care for the environment or the people living there.

Vietnam isn't a fan of China, so there is less of the China dams in Vietnam. I'd put that blame solely on Vietnam.