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Tides are the twice-daily rising and falling of the ocean at the shores of continents and islands. Over an approximately 12-hour cycle the tide in a locality flows out to low tide (ebb tide) and flows in to high tide (flood tide). The cycle is repeated again over the next 12 hours so that each day and each night there is a high and a low tide.

Tides also occur in all bodies of water on the earth. In some freshwater lakes, such as the Great Lakes, the tide may be only an inch or two, as most tides are too small to be noticed without instruments. In some places, tides are relatively shallow; in other places, the turning of the tide creates tidal rushes that ...

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