[NOTE: 8/4 Map updated to reflect accurate location of logjam. I received this image from one of the people who lost a boat there.]
I know there will be a lot of rafters on the upper Kenai River this coming weekend and I hope to help someone avoid disaster. This morning Jeff Varvil of Alaska Raft and Kayak told me that one of their customers pinned their rental cataraft in a pretty sizeable cottonwood that has fallen right in the channel of a popular braid on the upper river. I am attaching a map of the area as he described it to me (thanks Google Earth!). The exact location was given to me by someone who lost a boat in there.
A large cottonwood log is bridging the main channel and there is no way to avoid it by the time you can see it. I have been through there many times and the current smokes along pretty good in there.
Avoid the back channel altogether and just stick to the main channel on river right.
Hope it helps! Please chime in if you have more info.