New Zealand mudsnails (Potamopyrgus antipodarum; NZMS) are a widespread invasive species that was first discovered in Michigan’s inland waters in 2013 and since then they have been detected in Blue Ribbon trout streams including the Au Sable, Boardman, Manistee, Pere Marquette, and Pine Rivers. Surveys to document their initial densities in Michigan rivers were conducted in 2013 and 2014, but there is a need to better understand long-term effects of NZMS on the ecology of northern Michigan rivers. Therefore, the objectives of this study were to: (1) evaluate changes in macroinvertebrate assemblages over a 10-year period across river systems with NZMS, (2) characterize current benthic macroinvertebrate assemblages across a gradient of NZMS densities in northern Michigan rivers, and (3) understand inter-seasonal effects of NZMS on macroinvertebrate assemblages. In summers 2023 and 2024, surveys of benthic macroinvertebrates were conducted at 41 sites representing a gradient of NZMS densities (0/m2 to 39,000/m2) across multiple rivers. Sites were sampled in May and in August to assess inter-seasonal variation. Preliminary results suggest that sensitive benthic macroinvertebrates (e.g., Ephemeroptera, Plecoptera) remain prevalent, but decreased (31.7- 87.1% in density) compared to historical records. However, tolerant taxa (e.g., Diptera and Coleoptera) did not change over time. Inter-seasonal variation was observed, with NZMS densities 35-fold higher in August (39,000 per m2) compared to May (1,100 per m2). It appears that 10 years after the initial invasion of Michigan rivers, NZMS populations have increased, and may have a long-term impact on native macroinvertebrate assemblages.