I have done this rafting trip five times, and a lot depends on the weather that time of year. If you're lucky, there haven't been any super typhoons in the area for awhile, or a drought. If you're coming in after a big typhoon, the river can be pretty unpredictable and even the guides won't know where the rough parts will be. If it hasn't rained much in awhile, the water can be so low you will bottom out in areas and be hitting lots of rocks in others. The trip organizers and guides will tell you if it's a good time to raft, but the hotels and travel agents in town want to get people in the boats no matter what the weather.
If you've come at a good time, it can be great fun. You have to do a good bit of work to avoid hitting rock faces and avoid boulders, but the guides are attentive with their motorboats if any raft gets into trouble. That said, this isn't a walk in the park. I would say at times it can be pretty dangerous. Our raft has capsized at some point every time I've been. I've been dragged through boulder fields rather fast a few times. I relaxed, like the guides taught us, but I and my companions have been battered and bruised. They give us sturdy life vests and helmets, so we keep the harnesses tight.
I'd say the training is good, the equipment is maintained, and the guides are professionals. Everyone who has gone with me has said it's one of the best things to do in Taiwan. After you arrive in Hualien, there are many companies that will sign you up. They then arrange to pick you up at your hotel, take you to the river, show you a training video, get you in the boats with enough people, provide a lunch, provide a shower and changing room at the end, and then take you back to town. You'll be tired.
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