Other forms: sandbars
A sandbar is a long ridge of sand that's either underwater or rising just above the surface. When sailors are navigating close to the shore, they have to watch out for sandbars.
Sandbars form in rivers and oceans when moving water pushes sand or sediment up into a long, narrow slope. These natural formations are often submerged, which can make them hazardous for boats. During low tide, some ocean sandbars become exposed and provide a safe, dry way to walk out to a nearby island — at least until the tide comes in and the sandbar vanishes under the waves again.