This started out badly, in that they sent us in the van with a group for a different tour. The company did correct the situation very graciously to our satisfaction. But I suggest quizzing the tour operators before leaving their office, to ensure you are on the tour you've signed up, where it starts, where the lunch is, etc.
Kayaking started about 1.5 hours drive north of Chiang Mai. Water was more rapid than the very calm, relaxing kayaking trip we signed up for. This may have been because of the aforementioned mix-up. It was a bit of struggle to keep the kayak steered as needed through river debris, narrow white water like spots, etc. We did hit a submerged tree trunk and nearly toppled. The accompanying kayak guide had to come pull us off the tree trunk. The fast water requires full attention to kayaking and prevents you from enjoying nature and watching birds, etc. We did get to calmer water for about the last 20% of the trip. Getting the kayak's out at the meeting point and drive back to hotel took about 2 hours.