Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes
This publication presents findings from the De Salaberry water retention project, a 5-year study of a small, naturalized dam in southeastern Manitoba. Combining field monitoring with hydraulic and phosphorus reduction modelling, the study evaluates how site design and water retention time influence total phosphorus reduction and provides recommendations for future projects.
Key Messages
-
Water retention projects, such as conserved/restored wetlands or small naturalized dams, are critical for climate change adaptation in the Canadian Prairies as they reduce flood and drought risk while also improving water quality.
-
Many water retention projects currently in the pipeline are expected to promote phosphorus reduction benefits, but these benefits are unlikely to be maximized given standard design practices.
-
Future water retention projects should be designed more strategically to maximize phosphorus reduction by increasing water retention time and ensuring that runoff capture is targeted from phosphorus hot spots.
Excess nutrient loading from agricultural landscapes contributes to eutrophication and harmful algal blooms in freshwater systems across Canada, such as Lake Winnipeg. To better understand how natural infrastructure can help address this challenge, the International Institute for Sustainable Development monitored the De Salaberry water retention site in southeastern Manitoba between 2019 and 2023 to evaluate its phosphorus reduction potential.
The study found that the De Salaberry water retention site reduces phosphorus loads under many conditions while continuing to provide its primary flood and erosion mitigation functions. However, performance varied considerably between years and was strongly influenced by both incoming phosphorus loads and the retention time of water. The study also evaluated how adjusting outlet structure configuration and reservoir size can increase retention time, enhancing phosphorus reduction performance.
As investment in water retention infrastructure continues across Canada, integrating quantifiable phosphorus reduction estimates into project design and planning will be important for understanding their impact and meeting water quality objectives. The methods and findings presented in this study provide a foundation for integrating phosphorus reduction assessment into future site screening, design, and retrofit planning. With continued monitoring, broader validation, and more accessible design tools, naturalized water retention systems could play a stronger role in integrated watershed management and contribute more meaningfully to phosphorus reduction targets intended to prevent or reverse eutrophication in vulnerable freshwater systems.
Participating experts
You might also be interested in
The Value of Water Retention Beneficial Management Practices to Farmers and Landowners in the Seine Rat Roseau Watershed District
This report assesses the economic returns to communities and landowners from implementing on-farm water retention projects in the Seine, Rat, and Roseau watersheds in Manitoba, Canada.
Natural Infrastructure Essentials
On the Canadian Prairies, the need for water storage to cope with climate change is increasing. Natural infrastructure provides a solution.
Nature That Works
This publication shows how natural infrastructure can contribute to meeting water management needs, while also providing social, economic, and environmental benefits.
Over a Decade of Protecting the World's Fresh Water: Five ways IISD Experimental Lakes Area has made a difference
The Experimental Lakes Area has been transformed ever since IISD saved it from imminent closure. But, don’t just take our word for it. Here are five stories from people who have seen, firsthand, the impact of IISD-ELA over the last decade.