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Constructed wetlands help improve water quality through natural filtration and biological processes. As water slows down through the wetland, sediment settles, and nutrients are absorbed or broken down by vegetation and microorganisms. Wetlands also reduce erosion, store runoff, and create valuable wildlife habitat.

• Slow and store agricultural runoff, reducing flooding and erosion
• Filter sediment, nutrients, and other pollutants to improve water quality
• Provide an alternative use for wet or marginal lands
• Support biodiversity by creating food, shelter, and breeding areas for wildlife
• Offer upland habitat for pollinators when surrounded by native plants
• May help recharge groundwater by releasing water slowly into the soil

Together, these benefits make constructed wetlands a practical and environmentally valuable part of a sustainable farm or property plan.

• Naturally wet or marginal areas
  • Look for natural flow paths or low lying areas where water ponds after heavy rainfall
• Land underlain with poorly drained soils, such as clay or silty clay
  • Well drained sands and gravel are not suitable as they do not retain water
• Areas next to or within existing habitat features such as woodlots or wetlands

Conduct a test hole in the proposed wetland area to observe how water levels change over time; this will help indicate the water levels in the future pond.

Catchment size measures the area that will drain into the wetland, which determines how much water the wetland will capture. Catchment size can be estimated from topographical maps or surveys, and by examining drainage maps.

In areas where the natural slope favours water ponding, an excavation scrape may be sufficient to provide definition and adequate water storage to the wetland. When the slope does not favour water containment, a berm can help hold water in the wetland. The minimum height of the berm should range between 0.3-0.6 m above the maximum proposed water level in the wetland. Standpipes or control structures can be utilized as outlets to control the water level and manage excess water.

Consideration should be given to the type (groundwater, surface or tile) and amount of water that will feed into the wetland. Large scale runoff events may threaten the integrity of the wetland and should be integrated in the overall design plan. This should include the construction of a spillway to ensure the wetland is protected against potentially damaging amounts of water.

Material excavated from the pond area may be used to construct the berm if it contains a minimum of 10% clay.

Constructed wetlands vary in shape and size, depending on the site and the desired outcome. Irregularly shaped ponds are best suited to mimic the patterns and functions of natural landscapes.

Water depth influences the wetland vegetation and wildlife species. To enhance diversity, create shallow marsh areas along the shore of the wetland, and deeper pool sections towards the middle. Variable water depths maximize habitat, but at least 70% of the pond should be less than 1 m deep.

• Waterfowl prefer water less than 2 m deep for feeding habitat
• Provide spawning beds for some fish species
• Water 0.1- 0.5 m deep around the perimeter of the wetland provides habitat for sedges and cattails

• Limit freeze-up during the winter and allow opportunities for groundwater recharge
• Fish and amphibians require water 2-3 m deep in order to overwinter
• Submergent plants can thrive in deeper pools (2-3 m)

Enhance wetland areas by maintaining a natural buffer strip around the wetland. Planting a variety of native trees, shrubs, grasses and wildflowers in the buffer will attract more diverse wildlife. Here is information on聽recommended species to plant.

Water levels will vary seasonally. It is common for the wetland to dry up during summer months, when precipitation is limited and the groundwater table is low.

Start by covering the upland areas of the wetland with topsoil to help new vegetation take root. Around the pond, plant a mix of native trees, shrubs, grasses, and wildflowers to strengthen the wetland’s function and provide food and shelter to wildlife. Keep weeds under control by聽 mowing or carefully spot-spraying herbicide near young plants, but avoid getting spray on their leaves or stems and never apply herbicides broadly near open water.

Along the shallow shoreline, add a variety of aquatic plants to create habitat and naturally filter the water, though, over time, many species will establish themselves naturally. You can also place large rocks or logs in or near the water to give turtles and other wildlife places to bask. If your property already has a wetland that has become degraded, restoring or enhancing it can bring back its natural ability to natural ability to filter water, reduce flooding, and support local wildlife, especially in areas close to existing habitats.