A bog is a type of wetland that accumulates peat as a deposit of dead plant materials, often mosses, typically sphagnum moss. Bogs are one of the four main types of wetlands and are characterized by their acidic and nutrient-poor environment. They are generally found in cooler northern climates and are formed in poorly draining lake basins. Bogs occur where the water at the ground surface is acidic and low in nutrients, and they derive most of their water from precipitation rather than mineral-rich ground or surface water. Bogs have distinctive assemblages of animal, fungal, and plant species, and are of high importance for biodiversity, particularly in landscapes that are otherwise settled and farmed. Some key features of bogs include:

• Peat: Bogs are characterized by a continuous carpet of sphagnum moss, a species-poor herbaceous layer, low ericaceous, evergreen shrubs, and widely scattered and stunted conifer trees. The ubiquitous moss layer of bogs is dominated by sphagnum mosses, especially Sphagnum magellanicum, S. angustifolium, and S. fuscum.

• Water source: Bogs are defined by three main characteristics: rain and snow (rather than ground water and runoff) are the main water sources in true bogs.

• Acidity: Bogs are highly acidic, with a pH of less than 5 (7 being neutral), and are associated with waters containing no more minerals than are contained in rainwater, often the only source of water for a bog.

• Flora and fauna: Given their acidic environment, typical bogs have simple floras. Other than the peat mosses, or sphagnums, and heaths and other members of the family Ericaceae, there are a few sedges and grasses, such as cotton grass; insectivorous sundews and pitcher plants; and many orchids. Animals are not common on bogs.

Bogs are recognized as a significant/specific habitat type by a number of governmental and conservation agencies, and they can provide habitat for mammals, such as swamp sparrow and song sparrow, and herptiles that frequent bogs include eastern American toad, northern leopard frog, and garter snake.