Bottom-release dams impact downstream rivers, but inflowing tributaries may ameliorate some of the effects. We examined macroinvertebrate assemblages in a regulated river, the Little River in southeast Oklahoma, above and below two downstream tributaries. Sampling included replicated kick-net samples in riffles and habitat characteristics.  The diversity and abundance of macroinvertebrates in the Little River increased below the confluence of the unregulated tributary.   The regulated tributary was associated with variable patterns of macroinvertebrates in the Little River below the confluence.  Factors affecting the influence of tributaries on mainstem rivers can include differences in temperature and flow, including the effects of differing water release schedules between tributary and mainstem dams.