The skier should know how to swim, but he or she should wear a life jacket regardless of swimming ability.[11] Specially-designed life jackets or ski vests allow movement needed for the sport while still providing floation for a downed or injured skier.[17] The most common water ski injuries involve the lower legs, such as the knee, because a fall at high speed can create irregular angles of collision between the skier's body and the water surface. Another common cause of injury is colliding with objects on or near the water, like docks