Benthic cyanobacteria that produce toxins have been increasingly detected in streams and rivers across the globe, and the risk these cyanotoxins pose to public health have been well-documented. However, the ecological effects of toxin-producing benthic cyanobacterial mats, such as anatoxin-producing Microcoleus mats, on benthic macroinvertebrate communities and the potential for bioaccumulation of cyanotoxins within macroinvertebrate tissues are unclear. To examine differences in benthic macroinvertebrate community assemblages within and surrounding Microcoleus mats, we collected 6 rocks in a paired design (3 covered by Microcoleus & 3 covered by green algae within a 1 m radius) within three separate riffles along a 1 km reach of the South Fork Eel River in northern California on two dates in August and September of 2022. To determine the anatoxin levels in the tissues of the macroinvertebrates, we collected individuals from the target taxa (Perlidae, Hydropsychidae, Psephenidae, Gastropoda) representing a range of functional feeding groups within the riffle and froze them following a period of excretion. We identified all macroinvertebrate community assemblages to a family or genus level and examined variation in community indices (e.g., richness). Preliminary data suggest that Chironomidae, known for their resilience to unfavorable environmental conditions, are 1.8-3.8x more abundant per unit area within Microcoleus mats as compared to mats dominated by green algae on adjacent rocks. Examining the differences in benthic macroinvertebrate communities living within and outside of toxin-producing cyanobacterial mats can improve our understanding of the ecological consequences of benthic cyanobacterial mat proliferations.