Surface-water levels fluctuate seasonally. Flooding occurs in times of high rainfall, and drawdown occurs during dry periods, often exposing matted vegetation or mud. Freshwater marshes often exhibit mosaic surface patterns made up of pools or channels interspersed with clumps of emergent sedges, grasses, rushes and reeds, with bands of shrubs sometimes found along the edges. Submerged and floating aquatic plants are abundant where pools occur. Freshwater marshes are formed mainly by the infilling of ponds and shallow lakes.
Beavers also play an important fole in the formation of some marshes.
These are small but highly productive ecosystems, supporting an abundance of plants and animals. The largest marshes in Nova Scotia are the Tantramar Marshes or the Chignecto wetlands near Amherst. This region is unique in North America for its complex history and pattern of wetland uses.