Previous versions:

• Extent of wetland cover and wetland loss – 2021
• Extent of wetland cover and wetland loss – 2015

Wetlands are lands that are seasonally or permanently covered by shallow water, as well as lands where the water table is close to or at the surface. Wetlands lie at the interface of terrestrial and aquatic habitats and as a result possess a unique mixture of species, conditions and interactions. This makes wetlands among the most dynamic, biologically diverse and productive ecosystems on the planet. Wetlands provide habitat for a diverse array of species and provide a wide variety of ecosystem services that benefit people and the environment. These include shoreline stabilization, water purification, groundwater recharge and discharge, and flood control/ attenuation. Wetlands also help limit greenhouse gases in the atmosphere by acting as carbon sinks and they provide many recreational opportunities (e.g. bird watching, nature appreciation, hunting, etc). When wetlands are lost or degraded these important ecosystem services are diminished and can be challenging to replace.

Figure 1. Ontario’s ecozones and wetland coverage (MNRF 2017).

Canada has approximately 1.29 million km² of wetlands covering 13% of the country’s terrestrial area; representing close to one quarter of the world’s remaining wetlands (ECCC 2016). Twenty-five percent of Canada’s remaining wetlands (6% of wetlands world-wide) are found in Ontario. In Ontario, four major types of wetlands are recognized: marshes, swamps, fens and bogs (OMNRF 2020). The majority of the province’s wetlands are found in northern Ontario (Figure 1). The typology and methods used to calculate wetland area in Ontario, under-represents some wetland types such as submersed vegetation wetlands. The Hudson Bay Lowlands Ecozone has more than 20,000,000 ha of wetlands that account for 82% of the ecozone and is the third largest area of wetlands in the world (Keddy et al 2009). Great Lakes coastal wetlands provide globally significant migratory bird habitat and support many globally and nationally rare species and vegetation communities.

Despite their important values, wetlands continue to be lost. It is estimated that up to 70% of wetlands have been destroyed or degraded in settled areas of Canada (DUC 2021). Wetlands in southern parts of Ontario have been and continue to be drained for agriculture, filled for development, polluted by toxic runoff and damaged by artificial changes in water levels (Environment Canada 2010). In Southern Ontario (Mixedwood Plains area), 68% of the wetlands originally present were lost by the early 1980s (OBC 2010) and an additional 4% has been lost since this time (OBC 2015). Wetland loss has been greatest in southwestern Ontario, parts of eastern Ontario, Niagara and the Toronto area, where over 85% of the original pre-settlement wetlands have been converted to other uses. While land conversion is the primary cause of wetland loss in southern Ontario, pollution, invasive species, alteration to natural water levels and climate change also pose serious threats (Environment Canada 2010).

Figure 2. Ontario ecozones (red outline), ecoregions (black outline) and ecodistricts(grey outline) (MNR, 2009).

Notwithstanding some localized losses or alteration, the wetlands in the Hudson Bay Lowlands and central and northern regions of the Ontario Shield ecozones (Figure 2) are largely intact.

This indicator assesses changes in wetland extent in southern Ontario from 2000 to 2011, 2011-2015, as well as changes across Ontario between 2015-2020 based on updated land cover information.

Land cover information from the Ontario Land Cover v.1(OLC v.1) was used to assess changes in the extent of wetlands between 2015 and 2020 across the province. In previous versions of this indicator the Mixedwood Plains ecozone was the only area assessed (with the exception of Manitoulin Island) by using the Southern Ontario Land Resource Information System (SOLRIS 3.0; OMNRF 2020 in 2020 and SOLRIS 1.2 in 2015). The change analysis process provides both an updated spatial inventory and summaries of mapping class change (e.g. area of change from natural area to urban impervious).

In this application, change detection analyzes the decreases in vegetation greenness, focusing on loss, using satellite imagery for different time periods between 2000 and 2020. Changes identified during change detection were verified using orthophotography available between 2000 and 2015 as well as 2015 and 2020. The model maps large and dramatic loss well and with high certainty, but in some cases, smaller change events were not modeled with certainty, in these cases, those that occurred near  high certainty events were  flagged for manual review. Additional high certainty events were then identified through detailed examination of multi-date digital orthophotos. Although attempts were made to capture all major events, some remain undetected.

The total wetland area was calculated for each time period (2000-2011, 2011-2015, and 2015-2020) using a Geographic Information System (GIS). The area of wetlands lost in each ecodistrict across Ontario from 2015 to 2020 was mapped (Figure 3), as well loss in southern Ontario for the three timeframes (2000-2011, 2011-2015, and 2015-2020) (Figure 4).

Previous assessments (1982-2002) of changes in wetland cover excluded wetlands smaller than 10 ha and many Great Lakes coastal wetlands (DUC 2010). The current analysis addresses smaller wetlands but could miss the incremental loss of small areas along the edge of larger wetlands (i.e., areas less than 0.5 ha over a 5-year period). For these reasons, the results of the assessment of wetland loss since 2000 conducted for this analysis cannot be directly compared to previous assessments of loss for earlier time periods.

While this indicator assesses changes in the extent of wetland coverage, there is no comprehensive, landscape-scale data available for assessment of trends in the quality and function of remaining wetlands. The State of the Great Lakes Report 2022 indicates that coastal wetland habitats in Lake Superior and the northern shorelines of Lake Huron are generally in better condition and show fewer signs of impairment than wetlands in Lakes Erie and Ontario (ECCC and USEPA 2022).

Though not included in this indicator, wetland restoration and stewardship activities are often conducted by non-profit conservation organizations.

Download Extent of Wetland Cover and Loss 2021 summary data 

Related Theme(s)

• State of Ecosystems and Species

Related Target(s)

• Enhance Resilience

Related Themes:

Pressures on Biodiversity – Habitat Loss

Web Links:

Ducks Unlimited Canada – Ontario wetlands https://www.ducks.ca/our-work/wetlands/

Ontario Ministry of Municipal Affairs and Housing – Provincial Policy Statement, 2024 – https://www.ontario.ca/page/provincial-planning-statement-2024

Ontario Ministry of Natural Resources – wetland conservation https://www.ontario.ca/page/wetland-conservation

Environment Canada – wetlands of Ontario http://www.ec.gc.ca/tho- wlo/default. asp?lang=En&n=06269065-1

Ontario GeoHub – Southern Ontario Land Resource Information System (SOLRIS) 3.0 – https://geohub.lio.gov.on.ca/documents/lio::southern-ontario-land-resource-information- system-solris-3-0/about

The State of the Great Lakes Report 2019 (ECCC and USEPA 2021) https://binational. net/2020/06/03/sogl-edgl-2019-2/

References:

Cowardin, L. et al. 1979. Classification of Wetlands and Deepwater Habitats of the United States. US Department of the Interior Fish and Wildlife Service Office of Biological Services Washington, D.C. December 1979. Downloaded from https://www.epa.gov/sites/default/files/2017-05/documents/cowardin_1979.pdf

Cvetkovic, M., and P. Chow-Fraser. 2011. Use of ecological indicators to assess the quality of Great Lakes coastal wetlands. Ecological Indicators 11:1609-1622.

Ducks Unlimited Canada (DUC). 2006. Natural values: linking the environment to the economy – wetlands. [Available at: http://www.ducks.ca/assets/2012/06/nv6_wet.pdf]

Ducks Unlimited Canada (DUC). 2010. Southern Ontario wetland conversion analysis: final report. Ducks Unlimited Canada, Barrie, ON.

Environment Canada. 2010. Why wetlands? Environment Canada, Ottawa, ON

Environment and Climate Change Canada (2016) Canadian Environmental Sustainability Indicators: Extent of Canada’s Wetlands.

https://www.canada.ca/content/dam/eccc/migration/main/indicateurs-indicators/69e2d25b- 52a2-451e-ad87-257fb13711b9/4.0.b-20wetlands_en.pdf

Environment and Climate Change Canada and the U.S. Environmental Protection Agency. 2021. State of the Great Lakes 2019 Technical Report. Cat No. En161- 3/1E-PDF. EPA 905-R-20-044. [Available at www.binational.net]

Environment and Climate Change Canada and the U.S. Environmental Protection Agency. 2022. State of the Great Lakes 2022 Technical Report. Cat No. En161-3/1E-PDF. EPA 905-R22-004. Available at binational.net.

Keddy, PA, Fraser, LH, Solomeshch, AI, Junk, WJ, Campbell, DR, Arroyo, MTK, et al. 2009. Wet and Wonderful: The World’s Largest Wetlands Are Conservation Priorities. BioScience, 59(1), 39-5 Natural Resources Canada. 2011. Polarimetric RADARSAT-2 for monitoring Canadian wetlands.

Natural Resources Canada, Ottawa, ON. [Available at: http://www.nrcan.gc.ca/sites/www.nrcan. gc.ca/files/earthsciences/pdf/sarrso/pdf/polarimet_e.pdf]

National Wetland Management Plan,  Canadian Habitat Matters, 2024. [Available at: https://nawmp.wetlandnetwork.ca/Media/Content/files/Habitat%20Matters%202024%20Annual%20Report.pdf]

Ontario Biodiversity Council (OBC). 2010. State of Ontario’s biodiversity 2010. A report of the Ontario Biodiversity Council, Peterborough, ON. [Available at: http://www. ontariobiodiversitycouncil.ca/index.php/reports]

Ontario Biodiversity Council. 2021. State of Ontario’s Biodiversity 2020: Summary. A report of the Ontario Biodiversity Council, Peterborough, ON.

Ontario Ministry of Municipal Affairs and Housing – Provincial Policy Statement, 2020. [Available at: https://www.ontario.ca/page/provincial-policy-statement-2020]

Ontario Ministry of Natural Resources and Forestry (OMNR). 2019. Southern Ontario Land Resource Information System Version 3.0 – Ontario Ministry of Natural Resources and Forestry, Peterborough, ON.

Ontario Ministry of Natural Resources 2025. Ontario Land Cover version 1.0 – Ontario Ministry of Natural Resources, Peterborough, ON.

Ontario Ministry of Natural Resources and Forestry (OMNRF). 2017. A Wetland Conservation Strategy for Ontario 2017-2030.  [Available at: https://www.ontario.ca/page/wetland-conservation-strategy]

Wetland restoration

Story prepared by Nature Conservancy of Canada staff. Between 1800 and 2011, over 1.4 million hectares (about 55%) of wetlands in southern Ontario were lost. In some parts of the province, these losses were even more dramatic: Essex County in Ontario’s far southwest lost about 92% of its wetlands in this time, while Haldimand-Norfolk lost about 82%. Most of these losses were due to drainage for agriculture, development and transportation. Today, we can see that the impacts of these losses are …