Why is proper hydration essential before a dive?

Proper hydration before a dive is essential primarily because it significantly reduces the risk of decompression sickness. Decompression sickness, often referred to as "the bends," occurs when nitrogen bubbles form in the body during or after decompression from a dive due to rapid changes in pressure.

When divers are well-hydrated, their blood volume is maintained at optimal levels, which aids in the efficient transport of gases, including nitrogen. Adequate hydration helps keep the tissues of the body well perfused and facilitates the elimination of nitrogen from the body during ascent. This decreases the likelihood of bubbles forming and reduces the overall risk associated with ascending to the surface.

While other factors related to diving performance, such as buoyancy control and swimming speed, can be influenced by hydration, they are not the primary reason proper hydration is critical. Moreover, hydration does not directly impact night vision, as that is more related to available light and the eyes' ability to adapt to darkness.