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Introduction to Freshwater Wetlands

Aerial view of a wetland

Aerial view of a wetland (shaunl, iStockphoto)

Aerial view of a wetland

Aerial view of a wetland (shaunl, iStockphoto)

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Learn about the geology, chemistry and ecology of freshwater wetlands.

Wetlands are habitats that are either under water, or soaked with water part of the year. Freshwater wetlands include marshes, swamps, bogs and fens. 

Canada has about 1.29 million km2 of wetlands. This covers 13% of Canada's land. And this is about 25% of the wetlands in the world. 

25% of Canada's wetlands are in the Boreal Shield. 21% are in the Hudson Plains. 18% are in the Boreal Plains.

Map of wetlands in Canada
First Canadian Wetland Inventory (CWI) Map Based on Canadian Wetland Classification System, 2019 (Source: Remote Sens. 2019, 11(7), 842; 

Did you know?

Almost 80% of the Hudson Plains is wetland. The Hudson Plains curve around Hudson Bay and James Bay. They include land in eastern Manitoba, northern Ontario and western Quebec.

There were once many wetlands all over Canada. But over time, wetlands are becoming more rare. In southern Ontario, 68% of the original wetlands have been converted from their natural state. They are now used for things like agriculture and housing. In southwestern Manitoba, only about 25% of the original wetlands in the ‘pothole’ region remain. The good news is that in the northern part of Canada, most of the wetlands are intact.

Just because an area is wet, doesn’t mean it’s a wetland. The amount of water in a wetland can change depending on temperature and precipitation. This means we need to look at other things to determine if an area is a wetland or not. One way is to examine the soil. 

Wetlands have hydric soils. These are soils that are fully saturated with water. Hydric soils are also anaerobic. This means they contain very little oxygen. 

The absence of oxygen means this soil has different colours and textures than aerobic soils. Aerobic soils have large amounts of a form of iron (Fe) that makes soil a yellow, orange or reddish colour. Anaerobic soils have a different form of iron. This gives the soil a gray colour.

The plants that grow in wetlands need to have special adaptations. These allow them to grow in low-oxygen conditions. Cattails and bulrushes have these adaptations. If you see cattails and bulrushes, this is a good indication that the area is a wetland.

Cattails and bulrushes in a marsh
Cattails and bulrushes in a wetland around a small pond (Source: Pito Fotos via iStockphoto).

Wetlands are important to many animals. Some of these are familiar, like frogs. Some are less well-known. 

Every drop of water contains microscopic phytoplankton and zooplankton. These are important parts of the food chain. Phytoplankton are microscopic algae and diatoms that can create their own food. Zooplankton are microscopic animals that eat phytoplankton. 

The surface of the water and the wetland bottom are covered with insect eggs, larvae, and nymphs. Fish, amphibians, and reptiles depend on the habitat provided by wetlands. And many bird and mammal species use the water and its adjacent shores. 

Let’s look more closely at the different types of wetlands and some of the plants and animals found there.


Marshes are permanently or regularly covered in standing or slowly-moving water. Marshes are rich in nutrients

They have many kinds of emergent vegetation. These are plants that grow up through the water. They include reedsrushes, cattails and sedges. The roots of these plants are covered in water for most of the growing season. Marshes are the most productive type of wetlands. This means they produce more organic matter than other wetlands. 

Marshes are home to many protected species. These include the Bald Eagle, Sandhill Crane, Eastern Fox Snake and Fowler’s Toad. 

Bald eagle, Eastern Fox Snake and Fowler’s Toad
From left to right: Bald eagle, Eastern Fox Snake and Fowler’s Toad (Sources: David McGowen via iStockphoto, Peter Paplanus [CC-BY-SA] via Wikimedia Commons and Judy Gallagher via Wikimedia Commons).


Unlike marshes, swamps have trees and shrubs. Swamps may be flooded seasonally, or for long periods of time. Like marshes, swamps are also nutrient-rich and productive. 

Swamp plants include coniferous, or cone-bearing trees and deciduous trees. Swamps are most common in the southern part of Canada. Swamps are home to many protected species. These include the Eastern Prairie Fringed Orchid, Loggerhead Shrike, Red-shouldered Hawk and Blanding’s Turtle. 

Loggerhead Shrike, Eastern Prairie Fringed Orchid and Blanding’s Turtle
From left to right: Loggerhead Shrike, Eastern Prairie Fringed Orchid and Blanding’s Turtle (Sources: Canon_Bob via iStockphoto, US Fish and Wildlife Service [public domain] via Wikimedia Commons and Wirepec via iStockphoto).


Bogs are also known as peat bogs. They are a kind of peatland. Peatlands are wetlands that contain peat. Peat is a build-up of partly-decayed plants. The top 30 to 50 cm of a peatland is made up of mosses and other living plants. Under that layer is the peat, which can be up to 10 metres deep

Peatlands (2013) by Hinterland Who's Who (0:30 min.).

Did you know?

In some parts of the world, dried peat is harvested as a source of fuel!

In a peatland, the peat acts like a giant sponge. This makes it hard for water to drain through it. Poor drainage and decaying plant material makes bogs very acidic. The water in bogs only comes from precipitation

The high acidity and low oxygen in bogs makes it very difficult for plants to grow. This is why the biodiversity in peatlands is low. 

The main kinds of vegetation in bogs are sphagnum mosses. These are often called peat moss. Mosses are small, soft plants with small leaves. Mosses do not have roots. They absorb water through their leaves instead. 

Shrubs like heaths can also be found in bogs. Heaths have adaptations for living in acidic soil. Other bog plants include cotton grass, cranberry, bog laurel, leatherleaf, blueberry and Labrador tea. 

Peat bogs
Left: Peat bog covered in sphagnum moss, ON. Right: Scottish woman stacks peat slabs to dry as bricks to be used for fuel (Sources: Moorefam via iStockphoto and wanderluster via iStockphoto).


Carnivorous plants also live in peatlands. They include things like sundews, butterworts and pitcher plants. Carnivorous plants are interesting. They get the nutrients they need by catching and digesting small insects and spiders. They can do this using a sticky liquid or by trapping them in their leaves.

Sundew, butterwort and pitcher plant
From left to right: Round-leaved Sundew (drosera rotundifolia),Common Butterwort (Pinguicula vulgaris) and Northern Pitcher Plant (Sarracenia purpurea) (Sources: Michel VIARD via iStockphoto, Jörg Hempel [CC-BY-SA] via Wikimedia Commons and Westhoff via iStockphoto).

Did you know?

Peatlands cover over 1.1 million square kilometres, or about 12 percent of Canada. 

Bogs provide habitat for both migratory bird species and permanent residents. These include palm warblers, Lincoln’s sparrows, tree swallows and northern harriers. 

Some large mammals also live in peatlands. These include moose, white-tailed Deer, wood bison and caribou. Small mammals like bog lemmings, southern bog lemmings and Arctic shrews prefer bogs to other types of habitats.


Fens are a type of peatland. Unlike bogs, fens are fed by surface water and groundwater. This means the soil there is less acidic. Fens are not as low in nutrients as bogs, so they are more productive than bogs. 

The main kind of plant growing in fens are sedges. Trees like cedars, dwarf birches, black spruces, and tamarack can also be found there. 

Fens are more common in the northern part of Canada. Birds found in fens include Virginia rails, yellow warblers and swamp sparrows. Mammals include water shrews, star-nosed moles and muskrats. 

Did you know? 

In some parts of Canada, peatlands are called muskegs. This comes from the Cree word maskek and Ojibwe word mashkiig, meaning “grassy bog.”


This article from Canadian Wildlife Federation has information, videos, images and audio clips from Canada’s wetlands. 


This article from Canadian Wildlife Federation has information, videos, images and audio clips from Canada’s peatlands.


This page from Ducks Unlimited Canada explains how wetlands protect wildlife and ecosystems, and why they’re disappearing.

Northern Peatlands in Canada

This story map from Wildlife Conservation Society Canada illustrates the northern peatlands of Canada and explains why they are so important for both climate and biodiversity.

Muskeg (2018)

This article from the Canadian Encyclopedia explains the origin of the word muskeg, how muskeg is formed and why it’s important.


Amani, M. et. al. Canadian Wetland Inventory using Google Earth Engine: The First Map and Preliminary Results. Remote Sensing. 2019, 11(7), 842;

Government of Canada. (2016, January 14) Water sources: wetlands. 

Lahey, A. (2019, July 25). Wetland who's who: Do you know your bogs from your fens?. 

National Wetlands Working Group. (1997). Canadian Wetland Classification System. 

Peat and Peatlands. (n. d.). Peatland distribution.

Science Direct. Wetland Soil - an overview.

Southee, M. (2020, April 30). It’s time to start paying attention to Canada’s peatlands. Canadian Encyclopedia.