In this fast-paced adventure story set in the Canadian arctic, fifteen-year-old Inuit hunter Nick Thrasher comes face-to-face with a fearsome creature on a routine caribou hunt gone wrong. Part grizzly, part polar bear, this environmental mutant has been pegged the "grolar bear" by wildlife experts. Nick may have escaped this time, but it won't be his last encounter.

Then Nick's estranged half-brother, Ryan, offers to take him on a rafting

...

You get over the fear of death and the smell of fish; boredom is an issue, sure, but it's not the main one. The biggest problem with being trapped on a jellyfish is not being able to get away from everyone. Martha and everyone else living there don't know how they got there or how long they've been there or where they're going. They can't escape-- but they're going to try. Or die trying. -- adapted from jacket