The abundance and diversity of benthic macroinvertebrates (BMI) were measured across four streams that span a gradient of urban and agricultural land cover in south-central Ontario. For each stream, BMI surveys were carried out across three seasons for reference (upstream) and test (downstream) sites with chloride being a contaminant of interest to this study. While two of the test sites had stream chloride concentrations that exceeded national guidelines for chronic toxicity,
only the site with the highest proportion of urban land cover in its drainage area suggested compromised community compositions across all study seasons. Additionally, the impact of sodium chloride, the most common road salt type, was studied on freshwater biofilm communities under laboratory conditions, where biofilms at high concentrations of salt show a high degree of aggregation.