Slough (hydrology)

A slough (US ⁱ/sluː/, UK ⁱ/slaʊ/) is a wetland, usually a swamp or shallow lake, often a backwater to a larger body of water. Water tends to be stagnant or may flow slowly on a seasonal basis.

In North America, "slough" may refer to a side-channel from or feeding a river, or an inlet or natural channel only sporadically filled with water. An example of this is Finn Slough on the Fraser River, whose lower reaches have dozens of notable sloughs. Some sloughs, like Elkhorn Slough, used to be mouths of rivers, but have become stagnant because tectonic activity cut off the river's source.

...
Wikipedia