What is the difference between class IV and class III rapids?

The classification of rapids is based on the level of difficulty and risk they pose to rafters, and other whitewater enthusiasts. This classification takes into account, the river geography, gradient, volume of water, level of risk, difficulty of maneuver among other factors. 

The classes range from I to VI, with class I being the easiest and class VI called impossible, being class V, the most challenging and dangerous. In Arenal Rafting we are extremely demanding on safety, and have a well earned record of 100% survivors, so we rather not do tours on class V rapids. We only offer class II & III tagged as “Family Friendly”, and the class III & IV, as “Adventure Tours” or “Adrenaline Junkies”. So basically class IV means paddle harder and more chances of falling out the raft, a situation that is quite fast to be controlled by our professional guides and kayakers. In less than 5 seconds the team will pick you up, laugh about it and keep going, -that easy!