Class IV (Advanced). You can always tell when a rapid of this size is coming up. The guides will talk about it for days upstream. The night before, around the campfire, you’ll hear every tale of every boat that ever had trouble getting through it. Even if you miss all of that and don’t notice the name in bold print on the map, you’ll be able to tell it’s near when the guides get very quiet, very serious. A Class IV rapid will be powerful, with high waves, big drops, turbulent current, rocks requiring advanced boating skills to avoid. And passengers will likely get a good view of it (even if they go through it with their eyes closed), because the guides will often stop to scout the route through the rapid from shore. (Yahoo Factor: There’ll be shouts of exhilaration and cold water screams as everyone gets soaked, but most take a rapid this size very seriously and save their excitement until they’re safely in the quiet water below.)