The salinization of freshwater ecosystems by road salt is a pressing environmental problem in temperate climates. However, despite increasing awareness of this issue, the effects of chloride and sodium pollution (the main constituents of road salt) on phytoplankton communities are poorly understood. While past studies have shown that excessive salt can be toxic and cause osmoregulatory stress for freshwater organisms, little is known about how communities respond in the context of other urban stressors (such as eutrophication and warming). For example, there is potential for salinization to favor toxin-producing cyanobacteria, which can cause serious public health risks. Given these concerns, this study aims to characterize cyanobacteria sampled from a series of 50 stormwater ponds across Brampton, Canada in the summer of 2022. Flow imaging microscopy was used to count individual organisms and estimate the biomass of distinct cyanobacterial genera. The data were then analyzed to assess the relative biomass contributions of toxin producers in relation to increasing chloride concentrations. For example, ponds with higher salinity tended to have higher concentrations of Cylindrospermopsis sp., which are associated with the production of the potent toxin cylindrospermopsin. This research contributes to our developing understanding of how ubiquitous urban stressors such as salinization affect ecosystem health and risk of harmful algal blooms.