There were earlier agreements, but the Colorado River Compact was negotiated in 1922, after all 7 signatory states had been admitted to the union. They’ve pretty much been arguing about it and re-litigating it ever since, but as I understand it the main problem was that the rainfall estimates they used when drafting it were way too high. It just happened to be during an exceptionally wet time period that they took their measurements, and so they allocated water that never did come. And, yeah, they’ve known this for a long time.
There were earlier agreements, but the Colorado River Compact was negotiated in 1922, after all 7 signatory states had been admitted to the union. They’ve pretty much been arguing about it and re-litigating it ever since, but as I understand it the main problem was that the rainfall estimates they used when drafting it were way too high. It just happened to be during an exceptionally wet time period that they took their measurements, and so they allocated water that never did come. And, yeah, they’ve known this for a long time.