You should watch carefully for any signs of land. There are many indicators that land is near.
A fixed cumulus cloud in a clear sky or in a sky where all other clouds are moving often hovers over or slightly downwind from an island.
In the tropics, the reflection of sunlight from shallow lagoons or shelves of coral reefs often causes a greenish tint in the sky.
In arctic waters, light-colored reflections on clouds often indicate ice fields or snow-covered land. These reflections are quite different from the dark gray ones caused by open water. Deep water is dark green or dark blue. Lighter color indicates shallow water, which may mean land is near.
At night, or in fog, mist or rain, you may detect land by odors and sounds. The musty odor of mangrove swamps and mud flats carries a long way. You hear the roar of surf long before you see the surf. The continued cries of seabirds coming from one direction indicate their roosting place on nearby land.
There usually are more birds near land than over the open sea. The direction from which flocks fly at dawn and to which they fly at dusk may indicate the direction of land. During the day, birds are searching for food and the direction of flight has no significance.
Mirages occur at any latitude but they are more likely in the tropics, especially during the middle of the day. Be careful not to mistake a mirage for nearby land. A mirage disappears or its appearance and elevation change when viewed from slightly different heights.
You may be able to detect land by the pattern of the waves (refracted) as they approach land. By traveling with the waves and parallel to the slightly turbulent area marked “X” on the illustration, you should reach land.
Information courtesy of the U.S. Army Survival Manual