Sandbar

Sandbars are geographic features that form when silt-laden water slows down. They are an impediment to navigation

Flowing water, like rivers, and ocean currents, or lake currents, can carry silt, sand, and if the current is extremely strong, even gravel and boulders.

The size of the suspended material is proportion to the water speed. When geographic features make the water slow down, the suspended material drops to the bottom of the channel, forming a sandbar.

When a river, lake or ocean current shows increases in water speed it will pick up the silt or sand at the top of a sandbar, potentially scouring it completely away, or crawling it downstream. When the current shows a decrease in water speed new sandbars can be deposited, and existing sandbars can grow in size, or become shallower.