@GOODESkier the army corp of engineers works with the states, Indian tribes, etc. to control water flow/releases at the various dams based off fish migration/runs. The release of water downriver by us will lower the water temps. This is done over 1000 miles of river in multiple states and two countries. The water temp can be 20-30 degrees difference from us here in PDX vs in Canada.
I'm sure there is much better info out there but that is the way I understand it.
Still waiting to try ZO on the river. Soon...