We kayaked the end canyon section a couple of years ago. Level was around 9k, if I recall. It is about 4-5 mi long (4 to campground, ~5 to lake). The water is impressive. In fact, it is a wild ride. Huge whirlpools, waves, hydrolics. Forget swimming, I don't think you would like it. Flush drowning is a serious risk. At one point, the river is about 6' wide (with 9k blasting through it). No good eddie above it, either. My friend paddled it around 12k and said it was far easier higher. If you like squirting the hell out of your creeker, you will love this section. I was gripped. The campground keeper offered to drive me down to drop a truck at the take-out. He said it was the least he could do for a guy who was about to die.
I'm sure that at different levels it will change hugely. We had a terrible experience at the put-in, with one guy letting his boat get away with all his gear in it (after hiking 4-5 mi). The ensuing chase ended up with a split up group and a yardsale of gear down a highwater canyon. Questionable decision making and unecessary risks rounded out a sketchy day. Maybe your experience will be better. On a good note, the guy who let his boat go didn't lose a piece of gear (including both chacos), thanks to the heroic but misguided efforts of Dave S.
Oh yeah, there is a terminal hydrolic near the bottom of the canyon (at some levels). Go down river from the foot bridge at the campground to scout it. The narrow spot is NOT easy to scout from the trail, and is about 1 mi upriver from the bridge. The river goes through the slot as it banks right, then left in a big S turn. There is a large eddie on r right after the slot. The boat, with one float bag, took around 10 minutes to see the light of day after the slot. DO NOT swim here. The trail is far above the river, and the features look small. They are not. Escape in much of it is difficult at best. The section is definately boatable. I'm a big water wimp. Many would love it. I would not take a raft in there b/c of the slot. At low flows, you will be able to eddie left above the slot it looked like. If you can eddie above the slot, the carry around it will be easy (100' on bedrock/boulders). At 9k an eddie fence committed you to the slot from 300+ yds up river.
As mentioned, you can hire horse packers to pack you down the trail past the gorge.