About Wetlands

Duck Photo by Eric Dresser Frog Photo by Eric Dresser Musk Rat Photo by Eric Dresser

Wetland Functions and Values

Wetlands represent one of the most important life support systems in the natural environment. Wetlands provide services including:

  • A water filtration system – removing contaminants, suspended particles and excessive nutrients, improving water quality and renewing water supplies.
  • An irreplaceable habitat – nesting, feeding and staging ground for several species of waterfowl and other wildlife such as reptiles and amphibians, and also for many species at risk.
  • A high quality spawning and nursery area for many species of fish.
  • Natural shoreline protection – protecting coastal areas from erosion.
  • A reservoir – helping to control and reduce flooding through water storage and retention.
  • A source of oxygen and water vapour – playing a vital role in the natural atmospheric and climatic cycles.
  • Recreational activities – hiking, birdwatching and fishing.

People in Canoe Photo by Matt Young
Beaver Photo by Eric DresserStream Photo by Eric Dresser

Wetland Stresses

Low Water Photo by Maggie YoungThe importance of wetlands to both humans and ecosystems is increasingly being recognized; however, there are many direct and indirect stresses that continue to threaten habitats. Stresses can also be classified as natural or human-induced. Many wetlands are able to adapt to natural stresses, such as storms, ice damage and low water levels. Unfortunately, human-induced stresses often occur so quickly and drastically that wetlands are not able to fully recover.

Direct Stresses

Dredging Photo Courtesy of U.S. EPAPeat Extraction Photo by John Mitchell

Shoreline Hardening Photo by Graham BryanDirect stresses are those that occur within a wetland, such as dredging, filling, draining, and invasive species. They are usually human-induced, highly visible and can result in rapid changes to wetlands.

Pollution Photo courtesy of U.S. EPAGreat Lakes coastal wetlands are often located at river mouths and in protected areas which are also favourable places for harbours. As a result, dredging has historically occurred in wetland areas to allow the safe entry of boats. Deepening the water and removal of sediments can result in the destruction of wetland habitat. In the same way, draining and filling of small wetlands for urban development and to increase agricultural area results in significant losses of wetland area and function each year.

Invasive species are those that reproduce so aggressively that they displace native plants in the area where they have become established. Common invasive wetland plants include Purple Loosestrife, Eurasian Water Milfoil and Phragmites. Aggressive fish and wildlife can also be a problem. Carp, a fish introduced from Europe, damages wetland ecosystems while feeding and spawning by uprooting submerged vegetation and increasing the cloudiness of the water which decreases light penetration required for plant growth.

Indirect Stresses

Exotic Species Photo courtesy of U.S. EPAIndirect stresses are often less pronounced, causing changes to occur to wetland function and vegetation communities over a longer period of time. It is often difficult to pinpoint the exact source of these stresses.

Indirect stresses include runoff from upstream agricultural practices, sewage treatment plants and industrial sources which can cause loading of nutrients, sediments and toxic chemicals in downstream wetlands. Due to the collective contribution of sources, it is often difficult to remediate these problems. Fortunately, wetlands are able to assimilate some nutrients and toxic chemicals through plant uptake and the interaction of flowing water with microbial communities active in the wetland soils. These tiny organisms are able to transform and break down nutrients and some toxic chemicals.

Shipping Photo courtesy of U.S. EPAAnother indirect stress is lakewide water level regulation, which occurs on Lake Superior and, to a more significant extent, on Lake Ontario. Regulation is carried out to maintain water levels in the Great Lakes at a level appropriate to accommodate navigation, shipping, hydroelectric power and shoreline landowners. However, this means less natural variability in water levels, to which coastal wetlands have adapted over many years. Alternating high and low water levels often lead to more diverse plant communities: thus, consistent high or low water levels can cause less diverse systems by excluding those species that rely on periodic changes in water level.


Habitat Types and Species Protected

Great Lakes Wetlands Conservation Action Plan: a partnership to sustain Great Lakes WetlandsThere are a wide variety of wetland habitats and species that are protected throughout the Great Lakes by partnered conservation initiatives, including the Great Lakes Wetlands Conservation Action Plan (GLWCAP) and the Eastern Habitat Joint Venture. The five major freshwater wetlands types are represented in protection activities: marsh, swamp, bog, fen, and shallow open water. For each of the habitat types, examples of areas with secured sites and some of the protected species found within them are provided in the lists below.


Marsh Photo by Ducks UnlimitedThese wetlands are periodically or permanently covered by standing or slowly moving water. Marshes are rich in nutrients and are characterized by an emergent vegetation of reeds, rushes, cattails and sedges. Water remains within the rooting zone of these plants for most of the growing season. Marshes are the most productive wetlands habitat.

Areas with Secured Sites

  • Long Point Marsh
  • Matchedash Bay
  • St. Clair River
  • Detroit River
  • Dunnville Marshes
  • Wainfleet Bog
  • Niagara River
  • Metro Toronto's Waterfront
  • Oshawa's Second Marsh
  • Hamilton Harbour
  • Bay Of Quinte
  • Rondeau Bay
  • Big Sandy Bay
  • Hoasic Creek
  • Pigeon Marsh
  • Port Franks Wetlands And Dunes
  • Riley Marsh

Species Protected

  • Bald Eagle
  • Forester's Tern
  • Loggerhead Shrike
  • Prothonotary Warbler
  • Red-shouldered Hawk
  • Sandhill Crane
  • American White Pelican
  • Least Shrew
  • Eastern Hog-nose Snake
  • Eastern Foxsnake
  • Queensnake
  • Eastern Spiny Softshell Turtle
  • Spotted Turtle
  • Fowler's Toad
  • Orangespotted Sunfish
  • Spotted Gar


SwampSwamps are dominated by shrubs or trees. They may be flooded seasonally or for long periods of time. Swamps are both nutrient rich and productive. Vegetation may be composed of coniferous or deciduous forest or tall thickets. Swamps are most common in temperate areas of Canada.

Areas with Secured Sites

  • North Cayuga Slough Forest
  • Brockville Long Swamp Fen
  • Minesing Swamp
  • Oxley Poison Sumach Swamp
  • Westplain Mud Lake
  • Hoasic Creek (DuPont Provincial Nature Reserve)

Species Protected

  • American Ginseng
  • Dwarf Hackberry
  • Eastern Prairie Fringed-orchid
  • Least Bittern
  • Loggerhead Shrike
  • Red-shouldered Hawk
  • Blanding's Turtle
  • Spotted Turtle


Bogs Photo by Nancy PattersonBogs are peat-covered wetlands in which the vegetation shows the effects of a high water table and a general lack of nutrients. Due to poor drainage and the decay of plant material, the surface water of bogs is strongly acidic. Although they are dominated by sphagnum mosses (peat) and heath shrubs, bogs may support trees. More common in northern Ontario and rare in the south, bogs are the least productive of all wetland types.

Areas with Secured Sites

  • Wainfleet Bog
  • Fairlan Lake Bog

Species Protected

  • Virginia Bartonia
  • Many-fruited False Loosestrife
  • Marsh St. John's Wort
  • Pin Oak
  • Southern Tickseed
  • Swan's Sedge
  • Tapered Rush
  • Toadflax
  • Torrey's Mannagrass
  • Virginia Yellow Flax
  • Yellow-breasted Chat
  • Opossum
  • Black Ratsnake
  • Massasauga Rattlesnake
  • Spotted Turtle
  • Fowler's Toad


FenThese wetlands are characterized by a high water table with slow internal drainage by seepage down low gradients. Their surface waters may be acidic or alkaline. Fens are not as low in nutrients as bogs and as a result are more productive. Although fens are dominated by sedges they may also contain shrubs and trees. Like bogs, they are more common in the north.

Areas with Secured Sites

  • Brockville Long Swamp Fen
  • Westplain Mud Lake
  • Alliston Basin Wetlands

Species Protected

  • Handsome Sedge
  • Eastern Prairie fringed-orchid
  • Twin-scaped Bladderwort
  • Cooper's Hawk
  • Blanding's Turtle
  • Spotted Turtle
  • Olive Hairstreaked Butterfly

Shallow Open Water

Wetland Photo by Environment CanadaThese wetlands include potholes and sloughs (ponds), as well as waters along rivers and lakeshore areas. They are usually relatively small bodies of standing or flowing water commonly representing a transitional stage between lakes and marshes, or between spring high water levels and levels during the remainder of the year.

Areas with Secured Sites

  • Alliston Basin Wetlands

Species Protected

  • American Ginseng
  • Riverbank Wild Rye


Lands that are seasonally or permanently covered by shallow water, including lands where the water table is at or close to the surface. The presence of abundant water causes the formation of hydric soils and favours the dominance of either hydrophytic or water-tolerant plants. The five major types of wetlands are: marshes, swamps, bogs, fens and shallow open waters.
Natural Wetlands
A wetland dominated by native biota and occurring within a biophysical system which has developed though processes with minimal human intervention.
Disturbed Wetlands
A wetland that has had its functions altered, directly or indirectly, by external human or natural forces.
Enhanced Wetland
An existing wetland where some planned activity by humans addresses the stresses or limitations to change one or more functions or values.
Wetland Rehabilitation
Improvement of the functions or values of a degraded wetland.
Wetland Restoration
Modification of the existing function and structure of a wetland's habitat so that it is similar to historical conditions.
Wetland Creation
The conversion of a persistent upland vegetation community or ephemeral shallow water area into a permanent wetland where no previous wetland existed.
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