Guides can be cheeky, splashing water on their passengers and generally making fun.
Even without splashing it is highly likely that you will get wet up to the ankles at the very least. Luggage should be left behind, and any valuables should be securely sealed up in plastic bags.
Bamboo rafting is often offered as an extra in combination with elephant riding on a trek or day tour. The cost varies from place to place, and depends on the size of the rafts, how many passengers and how long the journey lasts, among other factors.
See any travel agency in Chiang Mai, and most guesthouses can organise a trip for you.
By Mark Ord.
The Travelfish newsletter is sent out every Monday and is jammed full of free advice for travel in Southeast Asia. You can see past issues here.