Which of the following is not considered an environmental aid for natural navigation?

Natural navigation relies on various environmental aids to help divers orient themselves and navigate underwater. Distinct rock formations, cloud patterns, and coastal landmarks are all reliable guides; they provide visible points of reference that can be recognized and used effectively when underwater or at sea.

Distinct rock formations serve as noticeable features that can be relied upon when determining one's location, especially in areas where other visual cues may not be available. Cloud patterns can also assist in navigation, as they reflect weather conditions and can indicate prevailing winds or changes that might affect navigation at the surface. Coastal landmarks provide essential orientation points, particularly when a diver is shallow enough to see the coastline.

Schools of fish, while interesting and important for ecological reasons, do not serve as stable or reliable references for navigation. Fish behavior can change rapidly due to various factors such as food availability, water conditions, or predator activity. As a result, they cannot be counted on as consistent points of reference, making them less effective as navigational aids compared to the other options listed.