Small part of a sea or lake partly surrounded by land. Chesepeake Bay.

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man-made channel of water connecting lakes, or rivers with the ocean.

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deep, steep-sided narrow valley.

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ocean reef made of coral and other animals. Like the rocks under the water in Hawaii, or where nemo lived.  Coral reef:

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 Round hollow shape usually at the top of a volcano.  Also see them google earth when you look at the moon or mars.

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