Long story short;
We were about 30yds away from a 16' cataraft that highsided a sweeper, then capsized it and sucked it under. It was on the upper Kenai just before the steep cutbank where the river gets a little deep and bends to the left (about 3/4 of the way from Sportsmans to Jims). It was that sweeper on the outside of the bend that I've always seen there.
The 2 passengers were able to jump off the cat and get to shore just as it highsided. The rower was still sitting in his seat when it flipped and went under. We had our throw bag ready, but he made it to shore after being under the boat for 5 seconds or so. When he got to shore I saw that he was wearing chest waders but no PFD (dumb!). I rowed like hell and we were able to catch their flipped cat floating down the river. When we got it to the next gravel bar and flipped it back over, this thing was a wreck. Oar snapped in two (no spare), lost a seat, lost their tackle, lost their anchor, destroyed their rear plywood deck with seats mounted on it. They finally hiked over to where we were and they accessed the damage. I let them borrow my spare oar until we hit Jims.
It was an eye opener and reminder to me that even on very tame rivers like the upper Kenai it is important to wear a lifejacket.