What does vigorous waving of an arm indicate?

Vigorous waving of an arm is universally recognized as a signal of distress. When someone is in trouble and requires assistance, they often use this method to attract attention, signaling to others that they are in a situation that may be life-threatening or that they cannot manage on their own. This action is specifically designed to convey a clear message that help is needed, making it an important indicator for rescue swimmers and other responders to initiate assistance as quickly as possible.

The other options might describe different scenarios, but they do not accurately capture the urgency and desperation conveyed by vigorous waving. For instance, requesting assistance could be a less frantic gesture, while preparing for rescue suggests readiness rather than a need for urgent help. In contrast, the wave signals an immediate need for intervention, which is why it is crucial for rescuers to recognize this behavior as a call for help.