Microplastics (MPs; < 5 mm) are a pervasive contaminant in freshwater habitats and biota worldwide. Terrestrial-aquatic subsidy exchanges can move anthropogenic litter into aquatic habitats where they may fragment into MPs and enter the food web. We sought to understand the importance of watershed land use and landcover (LULC), seasons, and river tributaries in connection to the abundances and compositions of MPs in river biota. We investigated if seasonal MP concentrations in freshwater biota vary with species traits and across a LULC gradient. Seventeen river tributaries in the Lake Michigan watershed with different dominant LULC were sampled seasonally for MPs in fish. Fish were collected using wading seine nets (n = 15 fish/taxon), euthanized, and preserved. Microplastics were extracted from fish by 1) digesting fish digestive tissues with potassium hydroxide, 2) fractionating samples to separate particles by size class, and 3) vacuum-filtering size class samples onto filters. A subset of recovered MPs will be picked from filters and analyzed for polymer type using ยต-FTIR spectroscopy. Preliminary results indicated that MP contamination was present in river fish and macroinvertebrate samples, with fibers contributing approx. 97-100% of all MP particles. Eighty-five percent of fish individuals across functional feeding groups (e.g., detritivore, zoobenthivore) contained an average of approximately 13 MPs/fish. There was a positive relationship between MP concentrations and fish trophic fraction, suggesting that MPs may move through the food web due to species trophic traits (X2= 14.18, P= 0.001). This study is anticipated to further reveal potential links of MP pollution in aquatic animals to environmental variables (e.g., season, LULC). This will inform targeted MP mitigation strategies for aquatic resources and increase our knowledge of the ecological consequences of MP pollution.