Approximate - nearest available gauge. Use as general reference only.
Note: Distance listed is NOT accurate or actual, but merely to sequence the photos/descriptions.
This trail/bridge is (approximately) at the 900' elevation contour (via topo maps), and lies 3,803' upstream of mouth (as measured online via GoogleMaps). Mean water-level elevation of Lake Superior is 602'. Thus, from this bridge to the lake, there would be ~298' of drop, making an 'equivalent' gradient somewhere in the 410-420 FPM range. (This is not to suggest anything regarding where the actual suggested put-in and take-out would be, but merely to provide some indication of drop here. Anyone having more/better measurements and info is very much welcome to provide their detail via comments below.)
Also, by my best measurements via online planimeter, drainage area at this point is only about 8 square miles. This should tell you how seldom this river will have enough flow to make any run possible. It will take peak snowmelt and/or significant rains to crank this up, and flow will drop off rather quickly. (Your window of opportunity will be extremely limited!)