Furthermore, friend and fellow-blogger Will Jordan reported that when he fished the Gallatin Canyon last weekend he saw floating fish in many holes. An inquiry with FWP revealed it was apparently the result of the flood (although other reports said the fishing was EXTREMELY good for the next few days). Here's hoping the kill wasn't too great an event.
There are times when anglers make poor decisions and get themselves in hairy situations, but something like this is hard to predict. My best advice would be to stay off islands and close to the banks if you know you're fishing below an ice jam. And get your line in the water ASAP afterward.