A mechanical warning flag system for a water ski boat. A first plate is coupled for rotation underneath the rope pylon. A second plate is coupled to the first plate and includes a vertical portion with an arcuate opening. A lever plate is pivotally coupled to the vertical portion of the second plate and includes a lever arm that receives one end of a bias spring and travels in the arcuate opening. The lever plate includes a pair of rope holders through which the tow rope is threaded. One rope holder is part of the pivotal connection, and the other is located on a distal portion of the lever plate. Since the lever arm is located between the rope holders, tension applied to the tow rope forces the lever plate downward thereby lowering the warning flag. In the absence of rope tension, a bias spring urges the lever plate upward to raise the warning flag.