shoal

shoal n Shoal, bank, reef, bar can all mean a shallow place in a body of water. In ordinary use

Shoal is applied to a shallow place, especially one that is difficult to navigate

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dangerous shoals in uncharted waters

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Bank, often as the plural banks, is applied to one that is formed by a muddy, sandy, or gravelly elevation but is deep enough to make navigation safe for lighter craft (as fishing boats)

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the Grand Bank, also called the Banks of Newfoundland, is a noted fishing ground

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and reef, to one where rock lies dangerously close to the surface

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the reef-bound shores of Bermuda

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Technically shoal is applied to elevations which are not rocky and on which the water is not more than 6 fathoms deep, bank to a similar elevation rising from the continental shelf and usually having a broad flat top under deeper water, and reef to a rocky elevation on which the water at low tide is 6 fathoms or less in depth.

Bar carries implications found in many senses (as of length, narrowness, and hindrance). It is applied to a ridge of sand or gravel piled up at and often across or nearly across a river's mouth or an entrance to a harbor and obstructing navigation.