Tis forTide

The tides are the rising and falling of the sea because of the pull of the moon and sun on the oceans. The depth of the water near the coast can change by several metres between high tide and low tide. At low tide a beach may have much, much more sand exposed than at high tide. The beach in the picture is at low tide. You can clearly see the dark mark on the jetty posts where the high tide comes to.