I visited Koprulu Canyon multiple times, and the main reason is river rafting. It would be best described as safe, amazing views, and adventurous. I came across many first timers (including my wife, friends, and tourists) who were reluctant to raft, and I had to provide them with basic advice for better results and experience...
My advice is to purchase special rafting shoes (TRY20) and avoid slippers or going barefoot. You could ask the tour bus driver to stop at any shop on your way. Small rocks and pebbles could cause minor injuries. Everyone must wear the floating jacket, although I find it useless because most of the journey you can actually stand while in the water (or if you happened to fall in the water). Most rafting tours provide lunch (dont expect much of quality) and remember the purpose is rafting! You get to jump in the water from 5 meters (only for the brave ones). Water temperature could be between 5 and 9 degrees Celsius in May.
Bring some extra clothes and a towel. Dont bring valuables or cameras/electronics. You could leave your bag in the vehicle (generally safe). There are changing rooms available. The entire journey is recorded on video so you might want to buy it at the end. There are also photos taken during your rafting adventure and you get to choose which one to buy.
Other activities are also available, trekking, canoe, etc. If you are going to ride a canoe, make sure you are a good (not professional) swimmer and travel in groups.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.