A Slough

1. (Britain) A muddy or marshy area.
2. (Eastern United States) A type of swamp or shallow lake system, typically formed as or by the backwater of a larger waterway, similar to a bayou with trees.
3. (Western United States) A secondary channel of a river delta, usually flushed by the tide.
4. A state of depression.
5. (Canadian Prairies) A small pond, often alkaline, many but not all formed by glacial potholes.