Restoration and Management at Rattray Marsh

Why Restoration Matters

Rattray Marsh is the last remaining lakefront marsh of its kind in the western Greater Toronto Area. Nestled in Mississauga, it provides vital habitat for wildlife and a natural retreat for residents and visitors alike.

To maintain the forests, wetlands and the Lake Ontario shoreline, ongoing restoration and management is essential. We work to protect the integrity of these ecosystems so they will endure for generations to come.

Threats Impacting Rattray Marsh

Rattray Marsh Conservation Area is bordered by residential properties and hosts over 300,000 visitors annually walking the trails and visiting the cobble beach. Urban greenspaces like Rattray Marsh Conservation Area are subject to many threats that include:  

• Climate change
• Human disturbances
• Pollution
• Invasive species
• Encroachment from surrounding properties

Restoration and Management Activities

Our restoration efforts at Rattray Marsh aim to:

• Improve water quality
• Restore natural aquatic, wetland, and terrestrial habitats
• Enhance biodiversity and ecosystem function
• Build long-term climate resilience

Habitat Restoration Activities

Extensive restoration efforts have been carried out at Rattray Marsh to enhance the ecological health and resilience of the marsh.

• Habitat Creation: New fish habitat and turtle basking areas were created to improve conditions for native wildlife, providing essential shelter and sunning spots for species that depend on these critical wetland features.

• Tree Planting: Over 12,000 native trees, shrubs, and over 150 wetland plants were installed, strengthening the natural vegetation community and improving water quality through filtration and shading.

• Carp Exclusion: Fencing was installed to deter and exclude adult common carp from sections of the marsh, preventing habitat disturbance and protecting aquatic vegetation from being uprooted.

• Emerald Ash Borer Management: To conserve existing tree canopy cover, select ash trees were injected with an insecticide to slow decline from emerald ash borer, maintaining important shade and a variety of tree sizes and heights.

• Purple Loosestrife Biocontrol and Invasive Plant Management: Galerucella beetles were released as natural biocontrol to help control purple loosestrife, reducing competition for native wetland species. In addition, CVC staff and partners managed priority invasive plant populations across key areas of the site to promote regeneration of native vegetation. We use a variety of techniques to manage invasive plants and where suitable volunteers help by hand pulling or weed wrenching priority herbaceous plants and shrubs during our community volunteer events.
• Wetland Habitat Improvement: We removed over 13,500 square metres of sediment from the marsh to improve water flow, water quality, and aquatic habitat. Removing the sediment also exposed the buried organic soils and

Ongoing Restoration Activities

We continually adjust our restoration techniques as needed to ensure long-term success. We are continuing to do the following:

Upstream Improvements

We’re working with landowners throughout the Sheridan Creek watershed to:

• Control erosion and reduce sediment flow
• Install stormwater management features
• Improve natural stormwater infiltration

Invasive Species Management

Many plant, insect and aquatic invasive species have become established at Rattray Marsh. We use an Integrated Pest Management Strategy to manage unwanted species. We currently manage priority invasive plants through mechanical (e.g. hand-pulling garlic mustard, weed wrenching invasive shrubs), chemical (e.g. targeted spraying of phragmites) and biological (e.g. beetle release to reduce purple loosestrife) methods to give native vegetation space to thrive.

We have strategically installed fencing in areas of the marsh to deter and exclude common carp. Carp continue to have access to Sheridan Creek and the central portion of the marsh. We periodically inspect and maintain the fencing to fix underwater breaches or toppled portions of the fence.

Tree and Shrub Planting

The marsh lost a lot of forest canopy when ash trees were killed by the invasive emerald ash borer. We have planted trees and shrubs to restore Rattray Marsh’s forest habitat. We set up temporary fencing around several pockets of newly planted trees and shrubs to protect them from wildlife browsing while trees and shrubs are young and getting established. We will remove the fencing once most of the trees’ branches and leaves are out of reach of wildlife, such as deer. 

We also use spray deterrents on trees and shrubs outside of the fenced areas. These sprays are derived from natural ingredients that deter animals, like rabbits, from chewing on newly planted trees and shrubs.

Monitoring our Restoration and Management Activities

We continually monitor the marsh to track improvements in water quality, forest health and wetland health. We continue to monitor native tree and shrub growth and survival in the restoration areas and plant more when needed

We’re also doing early detection monitoring for invasive forests pests, including hemlock woolly adelgid and oak wilt, to ensure we find and manage these invasive species before they become widespread.

Rattray Marsh is monitored as part of the Great Lakes Coastal Wetland Monitoring Program (GLCWMP), which assesses various indicators like fish, birds, vegetation and water quality. The Canadian Wildlife Service was involved in this program from 2010 to 2021, and we also conduct monitoring to evaluate restoration efforts, invasive species control and the establishment of new plantings. Our ongoing wetland monitoring focuses on issues like sediment buildup and invasive carp.

We’re developing a sediment budget for Sheridan Creek. Sediment is loose material, such as sand, silt, clay and small rocks. This sediment budget will identify where sediment is coming from and how fast it’s moving, and where it’s causing erosion or damage along the creek. The findings will be used to identify priority areas where we can take action to reduce un-natural build-up of sediment in the marsh. Too much sediment build-up can smother marsh plants, and harm the habitat that fish and wildlife depend on.

Enforcement

We employ in-house Security Officers. Security Officers assist with compliance messaging and may issue warnings to visitors, when warranted, for instances of non-compliance.

We have implemented the following solutions to help address challenges at Rattray Marsh.

• Use a dedicated security and compliance group to work alongside property management staff to help address compliance related occurrences.
• Collaborate with the City of Mississauga Security and Enforcement team for joint patrols and liaised with Peel Regional Police regarding prohibited activities occurring within the marsh.
• Increase enforcement patrols by CVC Security Officers and Provincial Offences Officers during peak season, including weekends and holidays.
• Plan enforcement blitzes to target prohibited activities including, but not limited to, dogs off leash, fireworks, use of bicycles and feeding of wildlife.

To report an occurrence, please contact us at 1-800-367-0890. CVC Provincial Offences Officers may issue fines under the Conservation Authorities Act (R.S.O. 1990, Chapter C.27) and Regulations as well as the Trespass to Property Act (R.S.O. 1990, Chapter T.21). For urgent matters please call 911.

Review our visitor rules for all Credit Valley Parks.

Frequently Asked Questions

What is the benefit of Rattray Marsh restoration?

Rattray Marsh is the last remaining lakefront marsh of its kind in the western Greater Toronto Area. Nestled in Mississauga, it provides vital habitat for wildlife and a natural retreat for residents and visitors alike. It is bordered by residential properties and hosts over 300,000 visitors annually walking the trails and visiting the cobble beach.

To maintain the forests, wetlands and the Lake Ontario shoreline, ongoing restoration and management is essential. Our restoration efforts aim to:

• Improve water quality
• Restore natural aquatic, wetland, and terrestrial habitats
• Enhance biodiversity and ecosystem function
• Build long-term climate resilience

We work to protect the integrity of these ecosystems so they will endure for generations to come.

Is Rattray Marsh an important habitat for wildlife?

Rattray Marsh provides important habitat for many species of birds, butterflies, amphibians, reptiles and mammals because of the scarcity of large natural areas along the Lake Ontario shoreline west of Toronto. The marsh is particularly important for migratory birds in the spring and fall. During this time, many birds travel across Lake Ontario and along the shoreline and stop at Rattray Marsh to rest and feed. This includes species of songbirds, ducks, geese, birds of prey, herons and shorebirds.

In general, Rattray Marsh will see more species of birds during the spring and fall migration periods than at any other time of year. For instance, birds destined to breed up north, like bay-breasted warblers, will find refuge at Rattray Marsh.

What is threatening the health of Rattray Marsh?

The ecological health of Rattray Marsh is subject to many threats and disturbances including:

• Climate change: increase in extreme weather including droughts, flooding, and storm events
• Pollution
• Invasive species: plants, insects, pathogens, animals
• Sedimentation accumulation in the wetland from upstream
• Human disturbance: people and dogs off trail, dumping of garbage, yard waste or unwanted pets, etc.

We continue to monitor and respond  through ongoing monitoring and management.

How are birds affected by emerald ash borer impacts and restoration efforts?

The invasive emerald ash borer (EAB) arrived in Mississauga in 2008 and since then has destroyed nearly all native ash trees in the area.

We began cutting down dead or dying ash trees in 2014 to ensure visitor safety from failing trees and to accelerate reforestation by planting a healthy diversity of tree and shrub species. Cutting down dead or dying ash trees resulted in changes to the bird community. With fewer ash trees, the forest canopy has opened, exposing the ground to more sun. Forest birds can still find refuge among the remaining trees or by moving to other areas of the conservation area where ash removal was minimal.

Some birds prefer open areas of the forest. Species like northern flicker, indigo bunting and great crested flycatcher will live in areas like this. Other birds, like song sparrow and American goldfinch, will use areas closer to the ground.

As the new trees and shrubs mature, the forest canopy will close. At that time, the diversity of birds that are attracted to the area will also shift.

To determine how the bird community has been impacted by EAB, we conducted breeding bird surveys in 2014 prior to ash tree removals, and again in 2022 after ash tree removals. Analysis is currently underway, but preliminary results suggest that most of the same species are breeding at Rattray Marsh.

Why were trees removed along the trails?

We identify and remove hazard trees along trails and in other public use areas. Hazard trees are weakened, dead, or dying trees that could fall and damage structures such as boardwalks and buildings, and pose a safety issue to staff and visitors. Rattray Marsh had an abundance of hazard ash trees because of emerald ash borer. These trees were felled to ensure park visitor safety along trails.

More information can be found in CVC’s Sustainable Forest Management Plan (2021-2040).

Why does the marsh smell sometimes?

Wetlands naturally produce odours as organic material breaks down. Dredging, the process of removing built-up sediment from the bottom of the marsh, and seasonal changes can temporarily increase this.

Will more dredging be needed?

Not at this time. We’re focused on upstream sediment control to prevent the need for future dredging.

How does urban development affect the marsh?

Rain and snowmelt, also known as stormwater, from roads and rooftops increases flow and sediment in Sheridan Creek. This is why upstream solutions are essential to protect the marsh.

What’s being done about invasive species?

We remove invasive species like phragmites and European buckthorn and then plant native species in their place. These management efforts are supported by staff and volunteers.

 

Why do we need to protect Rattray Marsh from common carp?

Common carp are an invasive fish species that was imported for eating from Europe to the United States and then to Canada in the 1880s.

Carp uproot plants as they feed, stirring up sediment, destroying aquatic vegetation and habitat, and ruining the quality of the water. They also lay and fertilize eggs among native plants, negatively affecting them.

Due to their large size, adult carp can dig up and harm wetland plants faster than plants can grow back. Plants are the foundation of the Rattray Marsh coastal wetland system and adult common carp cause significant harm to wetland health.

Why is there fencing around some of the trees and shrubs at Rattray Marsh?

Temporary fencing has been installed at Rattray Marsh around young trees and shrubs to protect them from excessive browsing by deer and other wildlife. This is called exclusion fencing, and it creates a safe zone where new plantings can take root, develop strong stems, and grow without repeated damage from feeding pressure.

The fencing will remain in place until the trees reach “free-to-grow” height, a stage at which most branches and foliage are above the reach of deer. Once the trees have matured beyond this vulnerable phase, the fencing will be removed, allowing the site to transition naturally into a self-sustaining and resilient plant community.

Why are there cameras and security patrols at Rattray Marsh?

CVC conservation areas may be under video surveillance for security, health and safety, or research purposes. Use of any personal information collected through video surveillance is protected and restricted through the Municipal Freedom of Information and Protection of Privacy Act, R.S.O. 1990, c.M.56, as amended. Learn more about our Privacy Policy.

A series of automated trail counters are deployed at entrances to Rattray Marsh. These infrared sensors count visitors entering and exiting the property and help to quantify visitation levels. While no identifying information is collected through the trail counters, this monitoring data helps us to  more effectively plan for enforcement activities, visitor services and trail improvements, and to better understand human use of the space.

How would a financial gift to Rattray Marsh make a difference?

A financial gift directly supports restoration, education and community engagement at Rattray Marsh. Your donation helps plant native trees and shrubs, remove invasive species, and maintain vital habitats that protect wildlife and water quality. Every dollar contributes to preserving this unique natural space for you and for future generations. All donations qualify for an official tax receipt. Make a lasting impact by supporting restoration and conservation efforts at Rattray Marsh all year round. Donate today: Credit Valley Conservation Foundation

To read more frequently asked questions about Credit Valley Parks, visit our Parks FAQ page.