We know the lakes and rivers in and around urban environments are contaminated by plastic debris, detergents, pesticides, heavy metals and other contaminants, but new research is showing that urban runoff toxicity is ill-defined and potentially underestimated globally. Researchers including Nathalie Tufenkji, Professor of Chemical Engineering at McGill University and Canada Research Chair in Biocolloids and Surfaces, are calling for cities to better manage and treat urban runoff to protect sources of drinking water and reduce the impacts on aquatic ecosystems.