NAVIGATING BY SEA COLOR AND THE SIGHTING OF FLOTSAM:
Sea color: A color change from the deep blue of the open sea to green may betray a familiar reef, enabling navigators to check their position.

Flotsam: Drifting wood or leaves betray land to windward, and drifting seaweed may indicate an upcurrent reef. A greenish tinge to the underside of a cloud reflects sunlight from a distant lagoon too far away to be seen.