Non-native brook stickleback (Culaea inconstans) have inhabited Turnbull National Wildlife Refuge (TNWR) in Washington state since at least 1999. Their impact on aquatic habitats is unclear and is of concern as TNWR is managed for migratory waterfowl and the diets of waterfowl and brook stickleback overlap. This study compared the benthic macroinvertebrate communities of four TNWR lentic systems that contain brook stickleback with five lentic systems that are free of brook stickleback. Each lentic system was sampled once in each of three periods in 2012 (June through September). Timing significantly affected macroinvertebrate density in the lentic systems that do not have brook stickleback but not in those containing brook stickleback. Summed across all taxa and samplings, lentic systems without brook stickleback had nearly 10-fold higher macroinvertebrate density (4.24 L^-1) and significantly more macroinvertebrate taxa than did lentic systems with the non-native fish (0.49 L^-1). To determine whether brook stickleback could contribute to changes in macroinvertebrate communities, we conducted feeding trials under laboratory conditions. Brook stickleback were presented with macroinvertebrates from 10 abundant taxa; the fish consumed, on average, 89% of the macroinvertebrates and consumed individuals from each taxon. We found no evidence of gape-limitation in brook stickleback for the commonly-encountered size range of macroinvertebrates. These results indicate that brook stickleback may be partly responsible for the altered macroinvertebrate communities at TNWR and that these non-native fish are a substantial threat to the quality of aquatic habitats at TNWR and should be considered for classification as invasive in Washington state.