I have been down this river 2 times with a local from White Pine. It is fun, beautiful and dangerous if you are not an experienced rider. The person that took us down the river has lived there his entire life and knows when and where to get off the river if there are bad areas. He would not take anyone down the river if he didn't think they were capable. We never had any issues and yes there were slushy areas, open areas, etc.
It sucks that the leader left his group behind. When we ride we are responsible for the person behind you. If they are not there, wait and then go find them. Most of our riding in the UP is off trail exploring and like Skylar we always prepare for the an overnight stay in the bush if something happens. I am glad they are all out and safe.