A slough ( /sluː/, /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, a slough can be 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.
In the Sacramento River, Steamboat Slough was an alternate branch of the river, a preferred shortcut route for steamboats passing between Sacramento and San Francisco. Georgiana Slough was a steamboat route through the Sacramento–San Joaquin River Delta, from the Sacramento River to the San Joaquin River and Stockton.