Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes

The report examines how natural infrastructure, such as wetlands and small naturalized dams, can be optimized to improve water quality in the Canadian Prairies. Using data from the De Salaberry project (2019-2023), the authors demonstrate that hydraulic retention time is the primary driver of phosphorus reduction. They argue that standard design practices, which prioritize flood mitigation, often overlook quantifiable water quality benefits. The document recommends integrating dynamic treatment models into planning to target phosphorus hotspots and optimize outlet structures to increase the time water remains stored before release.

• Water retention projects, including restored wetlands and small naturalized dams, serve as climate change adaptation tools in the Canadian Prairies by reducing flood and drought risks and improving water quality, with an estimated benefit of CAD 2.45 for every dollar spent.
• Phosphorus is identified as the key limiting nutrient responsible for algal blooms, making its reduction essential for improving water quality in waterways.
• Analysis of the De Salaberry project (2019-2023) indicates that hydraulic retention time—the duration water is stored before release—is the most critical factor for phosphorus reduction, as it allows more time for sedimentation and natural treatment.
• Modifying outlet culvert diameters can significantly impact phosphorus load reduction; for example, reducing the diameter from 600 mm to 400 mm increases the average flow-weighted retention time from 2.76 days to 4.14 days and increases total phosphorus load reduction from 271.3 kg to 309.9 kg.
• The document recommends that future projects prioritize locations that intercept high phosphorus loads and integrate flood mitigation and water quality objectives into a single design process to manage trade-offs between phosphorus reduction, flood risk, and construction costs.

APA

Simoes, J., & Grosshans, R. (2026). Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes. International Institute for Sustainable Development. https://www.iisd.org/system/files/2026-06/water-retention-reduce-algal-blooms-canadian-lakes.pdf

Chicago

Simoes, Joey, and Richard Grosshans. Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes. International Institute for Sustainable Development, 2026. https://www.iisd.org/system/files/2026-06/water-retention-reduce-algal-blooms-canadian-lakes.pdf.

Wikipedia

{{cite report |last1=Simoes |first1=Joey |last2=Grosshans |first2=Richard |title=Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes |publisher=International Institute for Sustainable Development |date=June 2026 |url=https://www.iisd.org/system/files/2026-06/water-retention-reduce-algal-blooms-canadian-lakes.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{simoes2026optimizing, author = {Simoes, Joey and Grosshans, Richard}, title = {{Optimizing Water Retention to Reduce Algal Blooms in Canadian Lakes}}, institution = {International Institute for Sustainable Development}, year = {2026}, month = jun, url = {https://www.iisd.org/system/files/2026-06/water-retention-reduce-algal-blooms-canadian-lakes.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }