I ran it three years ago in the Fall, after the major rain event that went through -- the estimated volume was 5k cfs. We were able to go over on the right with no real problems. My big (20') cat hung up briefly on the lip of the dam, but it slid off with a little bumping up and down. There was nothing in the way of a serious hydraulic to worry us in taking that route -- just a long smooth curler that pushed to river right.
There also appeared to be a route on the left, and I've had folks tell me that's better at lower levels. Even though they weren't visible at that level, I've seen pictures of sections of rebar sticking up in places on the top of the dam. They evidently are used to anchor boards that raise the water level for certain irrigation tasks. So you have to be sure to spot and miss them.
As to a portage, I suppose you could walk a kayak around. But carrying a raft and gear would be a different proposition. Better to take out at Swaseys and put in again at Green River.
And just for the record, this post in no way constitutes a recommendation to do what I did. It's entirely possible that at different levels this obstacle could present gear-damaging, life-threatening risks. FWIW.