What is the purpose of raising a hand by a lifeguard on the beach?

Raising a hand by a lifeguard on the beach primarily serves to indicate to swimmers that they should return to shore. This action is often used when there are safety concerns, such as dangerous conditions like strong currents, incoming waves, storms, or even the presence of a potential hazard in the water. The raised hand is a clear visual signal that alerts beachgoers to take action for their safety. It helps ensure that swimmers are aware of the lifeguard's instructions and can react promptly to avoid any potential dangers while in the water.

In contrast, other options, while potentially relevant in different contexts, do not capture the primary meaning of this signal as effectively. For instance, signaling for others to come closer may be relevant in some circumstances but does not specifically address safety. Demonstrating a rescue in progress would typically involve other gestures or flags and would not be conveyed simply by raising a hand. Lastly, a signal for a shift change does not apply in this scenario, as the focus of the hand raise is directed toward the safety of swimmers rather than operational changes in lifeguard duty.