The impact of treated sewage effluent on the hyporheos was investigated in 4 Ozark streams in northwestern Arkansas.  Samples were collected on 3 dates during the summer, at 4 stations on each stream.  One station was located above each sewage plant discharge and 3 stations were located downstream below each discharge at various distances.  Samples were pumped from narrow wells at depths of 5-20, 30-45, 60-75 and 100-115 cm below the stream bottom.  Invertebrate densities and taxon richness above and below the discharge points did not differ significantly.  Ordination and Spearman rank correlations indicated that community composition in the four streams is strongly dependent on DO availability which decreased with depth in the hyporheic zone.  Low DO levels in the hyporheic zone suggest that organic loading from nonpoint source runoff may be producing adverse impacts to the streams.