A new study finds that the Region of Waterloo’s $450-million investment in wastewater treatment upgrades has delivered measurable environmental gains, significantly reducing pollution and improving ecological health in Ontario’s Grand River watershed.
Completed in 2019 at two treatment facilities, including the Kitchener WWTP, the upgrades included a shift to fully nitrifying activated sludge systems. According to the January 2026 University of Waterloo study, that change led to a more than 80% reduction in total ammonia discharged to the river.
Drawing on more than a decade of biological monitoring data, researchers found that aquatic communities downstream of both plants increasingly resembled those upstream after the upgrades were completed — a key indicator of ecosystem recovery.
“This study reinforces the positive impact that the infrastructure upgrades have had on the health of the Grand River,” said Dr. Mark Servos, co-author of the study, Water Institute researcher and professor in the Department of Biology at the University of Waterloo, in a statement.
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The findings are based on a long-term biological monitoring program established by the Region prior to construction and maintained through 2022. Beginning in 2009, researchers sampled sites upstream and downstream of effluent outfalls at roughly three-year intervals using a before-and-after control-impact (BACI) study design.
The team focused on benthic macroinvertebrates — small organisms that live on the river bottom and are highly sensitive to water quality changes. These species form the base of the aquatic food web and are widely used as indicators of ecosystem condition.
Prior to the upgrades, macroinvertebrate communities downstream differed substantially from upstream sites. Following completion of the nitrification improvements, those differences steadily declined. Researchers concluded that improved effluent quality reduced ecological stress and supported recovery toward more natural conditions.
Adam Yates, a Water Institute researcher and study co-author, said the Region’s commitment to long-term monitoring was critical to detecting those changes.
“The resilience of river communities is astounding. This study shows that these communities just need us to take action to reduce pollution in order for significant recovery in ecological health to occur,” Yates said in a university statement.
While natural variation influenced upstream communities over time, the BACI study design allowed researchers to separate background ecological shifts from changes linked to the wastewater upgrades. That approach strengthened confidence that the recovery patterns were tied to the infrastructure investments.
Earlier research by Waterloo scientists had documented improvements in water quality and fish health following the plant upgrades. The new study extends those findings, demonstrating that benthic macroinvertebrates — a foundational component of the aquatic ecosystem — also responded positively.
The authors say the results underscore the value of pairing major environmental infrastructure investments with sustained biological monitoring to assess outcomes, guide policy decisions and demonstrate public return on investment.
The full study, Benthic Macroinvertebrate Recovery After Wastewater Treatment Plant Upgrades: Implications for Biomonitoring, is published in River Research and Applications.
