In extremely clear water, what is challenging to estimate?

In extremely clear water, estimating depth can be particularly challenging due to the lack of reference points. In environments with high visibility, divers may find it difficult to gauge how deep they are because clear water allows light to penetrate deeper, creating the illusion of distance. This can make it hard for divers to discern their actual depth without using instruments like a depth gauge.

In contrast, temperature, visibility, and current can often be assessed more directly. Temperature can be felt and monitored with thermometers, visibility can often be judged based on visual cues or objects, and current can usually be detected through movement or by observing the behavior of the surrounding environment. Hence, the clarity of the water complicates the depth estimation, making it the most challenging aspect in such conditions.