[0] Clearance [Kiteboarding] Clearance of at least 50 meters upwind (from any object) and 30 meters downwind (from another kitesurfer) is required. The risk of being blown into an airborne situation by a strong wind gust is real, effectively turning the kite boarder into an uncontrolled para-glider in risk of hitting any object downwind. [Windsurfing] 
Since there are no kite lines, no upwind or downwind clearance is required from any object other than a kite surfer or fishing lines, which means that windsurfers do not need to worry about 'rotor' or strong wind gusts. Also, they can emergency stop almost immediately. Experienced riders will do this by 'crashing' (with some risk to themselves) while beginning riders (who typically do not wear a harness) can depower the sail instantly by releasing the back hand or letting the mast fall on water. The risk of hitting hard objects or other water-goers is therefore minimal.