Shoal

In oceanography, geomorphology, and Earth Sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past and or present sedimentary and hydrographic processes are referred to as a shoal complex.

The term shoal is also used in a number of ways that can be either similar or quite different from how it is used in the geologic, geomorphic, and oceanographic literature. Sometimes, this terms refers to either (1) any relatively shallow place in a stream, lake, sea, or other body of water; (2) a rocky area on the sea floor within an area mapped for navigation purposes; (3) a growth of vegetation on the bottom of a deep lake that occurs at any depth; (4) and as a verb for the process of proceeding from a greater to a lesser depth of water.

https://en.wikipedia.org/wiki/Shoal