What signal indicates a lifeguard is entering the water for a rescue?

The signal that indicates a lifeguard is entering the water for a rescue is raising a rescue buoy above their head. This action serves multiple purposes: it makes the lifeguard's intention clear to others on the scene, ensures that the lifeguard is visible while they are entering the water, and conveys a sense of authority and preparedness. The rescue buoy is an essential lifeguard tool, indicating that the lifeguard is equipped to assist someone in distress.

While other signals like waving their arms or shouting for help could signify an emergency situation, they do not specifically communicate the lifeguard's intention to enter the water for a rescue. Running along the poolside may indicate urgency but does not serve to effectively communicate the action the lifeguard is about to take to those around them. Thus, raising the rescue buoy is the most effective and recognized signal for this critical action.