沙洲，是指河流、湖泊或沿海因波浪、水流、海流等堆积作用所形成的细长笔直的堤状砂砾沉积地形，通常在浅水处形成。

沙洲是河流中和海滨、湖滨带出露水面的沙滩。可以是河流中的心滩、江心洲、湖滨、海滨附近形成的沙滩等等。

在海商海事法律中，一般是指在河口处形成的沙堆，这些沙堆会限制某些种类的船舶不能到达上游的目的地。因此，往往需要将船上的一部分货物卸到驳船或小船上，使吃水变浅后才能通过沙洲完成航行。同样，船舶在上游港口装货时也只能先装一部分货物，其他货物要等船舶通过沙洲后才能再装上船。

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.