Before the pike slaughtering by the WDFW and the Kalispel Tribe began, I used to fish the POR regularly. Here is the site I used to know how high the water was.
http://www.popud.org/flow-and-elevation
You just have to look at the water level, which is the red line, and trace it back to the elevation on the left side of the chart. Once you get to know what the water looks like at a given elevation, you can check the site and know what you are going to see when you get to the river. I used to save photos to my computer of the fish we caught each day and note the water level in the photo file, that way I could see what water levels seemed to be the most productive.
Hope this helps
Good luck

http://waterdata.usgs.gov/usa/nwis/rt Great site once you figure out how to use it