River's guide to Swiss contains only selection of the best parts from this country. The swiss rivers are mostly navigable all the year round, because the rivers have water from a glacier, but the water is very cold. I advise to use a good raft, a helmet, a cork jacket and a neopren. The diffuculty is only informative by virtue of my experiences. I recommend to scout rivers from a bank, because the rivers often traverse by a dangerous gorge with forceful drop.