The Noun “Slough”

The Columbia Slough (near Portland, Oregon)

Garibaldi, Oregon

July 15, 2021

A slough (/sluː/ (listen)or /slaʊ/ (listen)) [to me it sounds like “slew”] 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 (the Fraser for example), 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.

In the Sacramento River, Steamboat Sloughwas 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.


A slough can form when a meander gets cut off from the main river channel creating an oxbow lake that accumulates with fine overbank sediment and organic material such as peat. This creates a wetland or swampenvironment. One end of the oxbow configuration then continues to receive flow from the main channel, creating a slough.

Sloughs are typically associated with the ridge formations found in their presence. Such a landscape consists of mosaic linear ridges, typically of some sort of grass such as sawgrass ridges in the Florida Everglades, that are separated by deeper water sloughs.

Edges of sloughs are layers of sediment deposited by a river over time. The development of this landscape is thought to occur by the preferential formation of peat in bedrock depressions. Multiple of these deposits mounted on top of the surrounding bedrock can become elongated alongside the slough and create flow diversions within the system. Different rates of this peat accumulation could be triggered by variations in microtopography that alter plant production and vegetation type. Water flow might be the key to preventing an accumulation of organic sediment in sloughs due to the fact that accumulation leads to lowering water depths and instead allows for the growth of vegetation.

In case you are wondering ….

Q. What are the differences between marsh, morass, bog, swamp, fen, mire, slough and everglade?

A. All these words denote wetlands of some kind, generally distinguished by their vegetation.

A marsh consists of grasslands in still or slow-moving water.

A swamp is forested: think of cypress trees, Spanish moss, shrubbery, vines, etc. A beaver dam generally creates a swamp.

A slough is a mixture of swamp and marsh, typically a backwater from a river.

A mire may be either a bog or a fen. The distinguishing feature of both is open, unforested wetland dominated by sphagnum (peat) moss. A bog typically is watered by rainfall, whereas a fen arises from groundwater. A fen is characterized by still ponds below ground level, a bog by little streams and small pools. In common speech the two words are often used interchangeably.

A morass is an impassable area in a swamp or a bog—deep, thick, waterlogged mud is its distinguishing feature. When disturbed the mud may liquify, turning into a quagmire or a “quaking” bog. A morass may occur in a swamp as well. When the mud is sandy it is called quicksand.

The Everglades are the enormous expanse of mixed tropical wetlands in southern Florida, consisting of swamp, marsh and lakes and slow-moving rivers. The word is a proper noun and always plural—thought to be a corruption of “River Glades.” There is no such thing as “an everglade.”

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