This dataset accompanies a paper submitted to Environmental Toxicology and Chemistry titled "Microparticles in Wild and Caged Biota, Sediments and Water Relative to Large Municipal Wastewater Treatment Plant Discharges". This study examined whether microparticle levels in resident fish, environmental samples, and caged organisms were elevated near the Waterloo and Kitchener WWTP outfalls along the Grand River, Ontario, Canada. All sampling for this work was done in October 2019. This dataset includes sample information for biotic and abiotic samples collected from the Grand River, a list of microparticles isolated from samples (including particle colour, morphology, and measurements), and information on chemical composition for a subset of particles.