What is a key risk associated with diving at night?

Diving at night presents unique challenges primarily due to reduced visibility, which can significantly impact a diver's ability to navigate effectively. This diminished light conditions can lead to difficulties in identifying landmarks, following a dive plan, and recognizing potential hazards in the underwater environment. As a result, divers may experience navigation errors, which can increase the risk of becoming disoriented or lost.

In contrast, the other choices do not pose the same level of concern. For example, the warmth of the water is generally not a risk at night; in some locations, water temperature may actually be more consistent. While it’s possible to encounter more divers in certain popular sites during nighttime, this is not a risk directly associated with the act of diving itself. Furthermore, the availability of emergency services may also be limited during nighttime hours, but the primary risk concerning navigation primarily stems from reduced visibility. Thus, the correct answer highlights the critical importance of understanding how reduced visibility can affect divers at night.