MARSH

[noun] - ground, esp. near a lake, river or the sea, that tends to flood and is always wetAt the mouth of the river is a large area of marsh. [U]This marsh supports a wide range of plants which need wet conditions. [C]Rain was falling fairly steadily and most of the ground had become a marsh. [C]Marsh gas is a gas produced in marshes by decaying plants that are covered by water.Marsh gas consists mainly of methane.