A bog is a wetland type that
accumulates acidic peat, a deposit of dead plant
material.
A marsh is a type of wetland,
featuring grasses, rushes, reeds, typhas, sedges, cat tails, and other
herbaceous plants (possibly with low-growing woody plants) in a context of
shallow water.
A marsh is different from a
swamp, which has a greater proportion of open water surface, which is
generally deeper than a marsh
A bog can be referred to as a
swamp while a marsh technically can not. Also the acidic waters of a bog
distinguish it as being different than a
marsh.