We rowed out of the lower salmon last august. It wasn't too bad, not really a lake, just very slow moving. I'm not sure where exactly you are talking about, but the slow water doesn't start until well below the confluence. I'm assuming you'd be boating the wild and scenic section? If you are doing the lower, a paddleboat would be a lot of work, as we had to keep at the oars. I'd watch for wind, start early in AM.
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye