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Bottom composition and formations Changes in bottom composition are something else to note during a dive. You may find that various areas have distinctly different bottoms, ranging from rock to sand, mud or reef, depending upon the environment. Plant life (discussed shortly) can vary with the bottom type. Even when the bottom composition is the same, water movement may create patterns you can use for navigation. Sand ripples are a good example; they form perpendicular to the water flow. In lakes