A bog is a wetland that accumulates peat, a deposit of dead plant material—often mosses, and in a majority of cases, Sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, quagmire and muskeg. Frequently they are covered in shrubs rooted in the sphagnum moss and peat. Bogs occur where the water at the ground surface is acidic and low in nutrients. Water flowing out of bogs has a characteristic brown color, which comes from dissolved peat tannins. In general the low fertility and cool climate results in relatively slow plant growth, but decay is even slower owing to the saturated soil. Hence peat accumulates. Large areas of landscape can be covered many meters deep in peat. Bogs have a distinctive group of plant and animal species, and are of high importance for biodiversity, particularly in landscapes that are otherwise settled and farmed.
A marsh is a type of wetland that is dominated by herbaceous rather than woody plant species. Marshes can often be found at the edges of lakes and streams, where they form a transition between the aquatic and terrestrial ecosystems. They are often dominated by grasses, rushes or reeds. If woody plants are present they tend to be low-growing shrubs. This form of vegetation is what differentiates marshes from other types of wetland such as swamps, which are dominated by trees, and bogs, which are wetlands that have accumulated deposits of acidic peat.
A swamp is a wetland that is forested. Many swamps occur along large rivers, where they are critically dependent upon natural water level fluctuations. Other swamps occur on the shores of large lakes. Some swamps have hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are “true” or swamp forests and “transitional” or shrub swamps. The water of a swamp may be fresh water, brackish water or seawater.