Microhabitat use by adult speckled dace (Rhinichthys osculus), adult longnose dace (R. cataractae), and juvenile dace (R. spp.) was investigated during the summer of 1992 in an Oregon Cascades stream. Selected areas were snorkeled day and night in order to evaluate differential use of habitat resources both temporally and spatially. Speckled dace were active both day and night but longnose dace were only observed at night when they were found primarily in fast flowing midstream areas. Small speckled dace (<8 cm TL) shifted from relatively fast flowing midstream daytime habitats to slower inshore areas at night. Large speckled dace (8-14 cm TL) used slower areas during the day and faster water at night. Potential competition between large speckled dace and longnose dace (8-20 cm TL) at night may be deflected by spatial microhabitat segregation. Within the fast water habitat at night, longnose dace used the fastest, shallowest areas with large substrates and were usually on the bottom. Large speckled dace used relatively slower, deeper water with smaller substrates and were near, but not on, the bottom. / Graduation date: 1994