What action should a lifeguard take upon witnessing someone diving into shallow water?

The appropriate action a lifeguard should take upon witnessing someone diving into shallow water is to immediately alert the individual about the danger. Diving into shallow water poses a significant risk of injury, including potential head or spinal injuries. By promptly notifying the person, the lifeguard can prevent a potential accident and promote safety in the aquatic environment. Quick intervention is essential, as it can help the individual avoid harm and make informed decisions about their actions.

In terms of the other options, ignoring the situation can lead to serious consequences if someone is injured. Jumping in after the diver may not be the best course of action unless a rescue is necessary, as it diverts attention from preventing the accident in the first place. Recording the incident for later review does not provide immediate assistance and neglects the urgent need for intervention in such a dangerous situation.