Good News: Fish Thriving in the Don Mouth after Naturalization

Back in 1987, the environmental degradation of Toronto’s waterfront was so severe, it was listed as an Area of Concern, and was at risk of impacting the wider Great Lakes Systems. Recently, following the completion of the Don Mouth Naturalization Project, we may have just restored our hope in the revitalization of Toronto’s aquatic ecosystems. 

OpenStreetMap, modified by Kelisi, Public domain, via Wikimedia Commons

Before the Don Mouth Naturalization Project took place, the Keating Channel by the Mouth of the Don River was at high risk of flooding. Its almost 90-degree angle design was ineffective to divert the Don River into Lake Ontario during big storms. Not only that, the land development around the Keating Channel also provided poor habitat for fish populations that led to a loss of fish diversity and populations in the area. 

Recently, following the completion of the Don Mouth Naturalization Project, Toronto Region Conservation Authority (TRCA), which has been closely monitoring fish populations around the Keating Channel area, found that fish populations have been slowly increasing and their habitats are looking better than ever!

The Don Mouth Naturalization Project design process was shaped by decades of community advocacy. Multiple assessments were conducted to facilitate the project’s main goals, which were flood protection and wildlife habitat restoration, all the while still allowing existing land use to continue. This project adopted a new and unique approach, where the river design came first, then the development planning followed. 

Don Valley Brick Works Park, by V. L., CC0, via Wikimedia Commons

Since the project completed, TRCA has been actively monitoring the aquatic landscapes and the health of the aquatic ecosystem in the area. TRCA conducted multiple fishing surveys in and around the area of the naturalization project. They found a significant increase in fish species, populations and diversities. It’s exciting to note that the Atlantic Salmon was recently found in the area. They were previously considered to be endangered and have not been sighted for a long time. It is safe to say the fish are enjoying the new channels and using this as their seasonal commute route to go from the Don Mouth River to the lake. 

In addition to the fishing surveys, TRCA has also been conducting turbidity monitoring, wetland monitoring and vegetation surveys to ensure the habitats are slowly being restored to sustain better aquatic health and support more fish populations and diversity. 

Overall, it is great news to have the fish back to their natural habitat! As the Don Mouth Naturalization Project continues to show promising results, TRCA will continue their monitoring and will update the public as they gather more data on the ecosystems around the area.

The story continues: to learn about the dry land restoration of the Don Mouth, join TFN’s free Zoom lecture on October 6, 7:00 pm, when we host TRCA speakers to tell us about the plants, birds and other animals now returning to the Don Mouth lands.

To learn more about the underwater restoration success of the Don Mouth, see:  

Sept. 2025 video of a TFN guest lecture; 

this summary in October 2025 newsletter

by Chloe W.

Toronto Field Naturalists wishes to acknowledge this Land through which we walk. For thousands of years, the Land has been shared by the Wendat, the Haudenosaunee, and the Anishinaabe. Toronto is situated on the Land within the Toronto Purchase, Treaty 13, the traditional and treaty Lands of the Mississaugas of the Credit First Nation. This territory is also part of the Dish with One Spoon Wampum, a covenant agreement between Anishinaabeg, Haudenosaunee, Wendat peoples and allied nations to peaceably share the land and all its resources. Today, the Land is home to peoples of numerous nations. We are all grateful to have the opportunity to continue to care for and share the beauty of this Land.