This same story played out a hundred years ago in the USA, see the Colorado River Compact. I would initially guess it's a problem now for the rivers you mentio

This same story played out a hundred years ago in the USA, see the Colorado River Compact. I would initially guess it's a problem now for the rivers you mention because only now do these places have the capital & use for a dam. And, really, fights over water never end. It's a difficult good- vital to life, inexpensive to divert, and yet both limited & temporal in supply, & difficult to relocate. Additionally, the source is frequently within another state or country. No one has been terribly successful yet in implementing water markets, and no one has conjured a perfect way to apportion water rights- with right of first use & riparian rights both having obvious flaws. Crazy things happen with water. For example, where I live I am not allowed to capture the water that falls on my own property. It's owned by someone else, and I can be prosecuted for capturing it (with a loophole for garden rainbarrels)