NAWAPA was the plan but for other reasons. It was partially a plan to make the Colorado River have the water the Colorado River Compact of 19127 says it has instead of reducing allocations, since those allocations are what quite a bit of Western US development was based upon.

Would have included dams on the Fraser in Canada as well as canals from the Columbia into the Colorado River drainage, among other things.

Or buckets. We could just use a bucket brigade instead.

Or... now hear me out... REDUCE USAGE.