Fighting the Invasion of Rattray Marsh

Rattray Marsh needs restoration, according to ecologists at Credit Valley Conservation (CVC). Known to many as Mississauga’s ecological gem, the marsh has seen a steady invasion of non-native carp over the decades, destroying the native ecosystem. This spring, CVC, with support provided by the Government of Ontario, will begin blocking carp from the marsh to help return it to its former health.

Carp are native to the rivers and lakes of Europe and Asia and were introduced to the Greats Lakes as early as 1879. They impact the marsh in three ways. Carp compete with native fish like catfish and suckers for food. They uproot underwater plants that predatory fish like pike and bass use to hide and ambush their prey. Carp kick up a lot of sediment, making the water murky, reducing the amount of sunlight and limiting the growth of new underwater plants required by fish, amphibians and birds.

“Blocking carp from the marsh is a big task,” said Bob Morris, Manager of Natural Heritage at CVC, who has been working on the project since 2007. “Our plan is to use proven methods to make sure only carp are excluded and native fish can still move freely between the marsh and the lake.”

CVC plans to control the invading fish by installing a number of traps and barriers where the marsh meets Lake Ontario. Each fish species in the marsh has a different spawning and migration period. CVC ecologists monitor the movement of different fish species and can predict when carp will move in and out of the marsh. The control measures will only be used when carp are known to be on the move.

CVC’s plan comes as welcome news to residents near the marsh who have complained about its degrading state for years. CVC, the Region of Peel and the Rattray Marsh Protection Association met with local residents on November 28 to discuss plans to restore the marsh. CVC presented a multi-year plan to tackle the most pressing environmental concerns.

“Controlling invasive species like carp is one front in our fight to restore the marsh,” said Pat Mullin, CVC Chair and Regional Councillor for Mississauga’s Ward Two. “We’re working to remove the sediment that’s burying the marsh and partnering with like-minded organizations upstream to stop more sediment and pollutants from entering.”

Over the decades, upstream development around Sheridan Creek has changed the marsh by contributing excess sediment, burying the native marsh ecosystem. This has resulted in poor water quality and loss of water depth, making it difficult for native fish to survive. Carp thrive in these conditions. Visitors to the marsh will notice the surrounding habitats appear quite healthy. The real ecological problems lay just below the water’s surface.

CVC is seeking volunteers to help set up some of the carp traps and barriers this spring. Those interested in volunteer opportunities at Rattray Marsh are asked to contact Annabel Krupp, Volunteer Program Coordinator, at 905-670-1615 ext.446 or [email protected].

Restoring Rattray Marsh coincides with a number of environmental restoration initiatives along Mississauga’s shoreline. Naturalization projects at Lakeside Park, Marie Curtis Park, Rattray Marsh and the proposed waterfront park at Lakeview all tie into CVC’s comprehensive strategy to restore the Mississauga shoreline. CVC’s Lake Ontario Integrated Shoreline Strategy (LOISS) engages governments, agencies, environmental NGOs, residents and businesses to build awareness of the environmental challenges facing the shoreline to find ways to restore it. More information on LOISS is available at

Invasive carp:


Credit Valley Conservation Foundation is a registered environmental charity that raises funds in support of the conservation projects of Credit Valley Conservation (CVC). Conservation Authorities are a provincial/municipal partnership. CVC was established by an act of the province in 1954 with a mandate to protect all natural resources other than minerals in the area drained by the Credit River. We have been working for almost 60 years with our partner municipalities and stakeholders to protect and enhance the natural environment of the Credit River Watershed for present and future generations.

Media Contact
Jon MacMull
Marketing & Communications Specialist
Valley Conservation
905-670-1615 ext. 385
[email protected]

Information Contact:
Bob Morris
Manager, Natural Heritage
Valley Conservation
905-670-1615 ext 435
[email protected]

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