Which safety measure is crucial when swimming in deep water?

Wearing a lifejacket is crucial when swimming in deep water because it significantly enhances safety by providing buoyancy and support, helping swimmers stay afloat in an environment where they may struggle. This is particularly important for those who may not be strong swimmers or are inexperienced, as it can prevent drowning incidents and allow for additional time to signal for help if needed. Lifejackets are specifically designed to keep a person's head above water, allowing them to breathe and remain safe while enjoying aquatic activities.

In contrast, the other options do not adequately address the potential dangers associated with deep water. For example, swimming without a buddy increases the risk of drowning since there is no one present to assist in an emergency. Staying close to the edge of the pool may not always be feasible in deep water situations, where swimmers may inadvertently venture into deeper areas. Lastly, while taking regular breathers is a good practice for endurance and avoiding fatigue, it does not directly enhance safety in deep water compared to the life-saving features of a lifejacket.