Marshes are frequently or continually flooded wetlands characterized by emergent herbaceous vegetation adapted to saturated soil conditions, changing water flows, and mineral soils. Marshes contain shallow water varying from 15 to 90 cm in depth. Expansive stretches of open water are uncommon and islands of vegetation are often present. Marshes are the most common wetland type in North America.

Marshes are separated into freshwater and saltwater types. Freshwater marshes are primarily inland, while salt marshes line the coasts of North America. The main freshwater marsh areas in Canada are the prairie potholes and the Great Lakes marshes. Coastal salt marshes lie along Hudson and James Bay, as well as the Atlantic, Pacific and Arctic coastlines.