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Old English mersc, merisc "marsh, swamp," from West Germanic *marisko (cf. Old Frisian and Old Saxon marsk "marsh," Middle Dutch mersch, Dutch mars, German Marsch, Danish marsk), probably from Proto-Germanic *mari- "sea" (see mere (n.)).
An area of low-lying wetland in which the level of water is generally shallow and often fluctuating. The water may be either standing or slow-moving. The water in a marsh is also more or less neutral or alkaline, in contrast to the water in a bog, which is acidic. The environment of a marsh is in general well-oxygenated and nutrient-rich and allows a great variety of organisms to flourish. In contrast to a swamp, in which there is an abundance of woody plants, the plants in a marsh are mostly herbaceous. Reeds and rushes dominate the vegetation of marshes. See also salt marsh.