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| ultraviolet radiation (1) | Ulva species (18) | Ulva species = Ulva spp. (1) |
| Ulva species. Enteromorpha species (1) | Ulva species: Enteromorpha species (3) | Ulva spp. (3) |
| Umpqua (3) | Umpqua River (1) | Umpqua Aquaculture (2) |
| Umpqua Bay (1) | Umpqua chub = Oregonichthys kalawatseti (7) | Umpqua chub = Oregonichthys kalawatseti (10) |
| Umpqua chub=Oregonichthys kalawatseti (2) | Umpqua dace = Rhinicthys cataractae (10) | Umpqua dace=Rhinichthys evermanni (3) |
| Umpqua dace=Rhinicthys cataractae (2) | Umpqua Dunes (1) | Umpqua Eden (3) |
| Umpqua Estuary (9) | Umpqua Fish Hatchery (1) | Umpqua formation (7) |
| Umpqua Indians (4) | Umpqua Jetty (1) | Umpqua Lighthouse (2) |
| Umpqua Lighthouse State Park (3) | Umpqua Narrows (1) | Umpqua National Forest (7) |
| Umpqua North Complex fires (1) | Umpqua pikeminnow = Ptychocheilus oregonensis (1) | Umpqua pikeminnow = Ptychocheilus umpquae (5) |
| Umpqua pikeminnow=Ptychocheilus umpquae (2) | Umpqua River (522) | Umpqua River Basin (168) |
| Umpqua River Basin, Brown Juga = Juga spp.. aquatic invertebrates, molluscs, gastropods, taxonomy, genetics, molecular biology (1) | Umpqua River Basin, Coquille River Basin, aquatic invertebrates, restoration ecology, natural resource management, metrics, ecosystem modeling (1) | Umpqua River Basin, Elliott State Forest, coastal hazards, landslides, sediments, geology, paleosciences, erosion, precipitation, climate, mathematical modeling, theses (1) |
| Umpqua River Basin, human impact, jetties, species list, navigation (1) | Umpqua River Basin, hydrology, climate, precipitation, temperature, mathematical modeling (1) | Umpqua River Basin, North Umpqua River, Rogue River, South Umpqua River, molluscs, gastropods, anatomy, genetics, taxonomy, new species description (1) |
| Umpqua River Basin, South Umpqua River, Stouts Creek, Callahan Creek, hydrology, soils, forest fires, erosion, theses (1) | Umpqua River Basin, Umpqua River, Calapooya Creek, South Umpqua river, Deer Creek, Myrtle Creek, agriculture, land ownership, natural resource management, ecological values, (1) | Umpqua River Basin, Yellowstone River Basin, Yampa River Basin, Manic 5 River Basin, hydrology, climate, precipitation, temperature, mathematical modeling (1) |
| Umpqua River Basom (1) | Umpqua River Bridge (1) | Umpqua River estuary (415) |
| Umpqua River estuary, human impacts, climate, habitats, land use, salinity, sea level, wetlands, wetland vegetation (1) | Umpqua River estuary, human impacts, climate, habitats, land use, salinity, sea level, wetlands, wetland vegetation, zonal distribution (2) | Umpqua River finger jetty (2) |
| Umpqua River Ranger District (1) | Umpqua River, Alsea Bay, Siletz Bay, (1) | Umpqua River, Drain (Or.), historical, photograph, transportation, (1) |
| Umpqua River, Eel River, Mono Bay, Monterey Bay, San Pedro Basin, Santa Monica Basin, hydrology, sediments, iron, agriculture, nutrients (1) | Umpqua River, Highcap lanx = Lanx alta, aquatic invertebrates, molluscs, limpets, taxonomy, morphology, genetics, anatomy, molecular biology, geographic distribution (1) | Umpqua River, historical, photograph, transportation, (1) |
| Umpqua River, hydrology, climate, precipitation, coastal hazards, flooding, geology, sediments, (1) | Umpqua River, Johnson Creek, Paradise Creek, West Fork Smith River, Beaver Creek (WFS), Crane Creek (WFS), Moore Creek (WFS), Skunk Creek (WFS), Upper Creek (WFS), Coquille River Basin, Coho salmon = Oncorhynchus kisutch, habitat restoration, (1) | Umpqua River. (1) |
| Umpqua South Jetty (1) | Umpqua squawfish = Ptychocheilus umpquae (8) | Umpqua squawfish=Ptychocheilus umpquae (3) |
| Umpqua State Wayside (1) | Umpqua triangle (3) | Umpqua Volcanics (1) |
| Umpqua Wayside (1) | Umpqua-Eden (5) | Undersea Gardens (1) |
| Union Creek (2) | United States (63) | Unpqua River (1) |
| Upland Takelma Indians (1) | Upogebia macginitieorum (1) | Upper Alsea River (1) |
| Upper Coos Indians (1) | Upper Coquille Indians (1) | Upper Cow Creek (1) |
| Upper Deschutes River (1) | Upper Devils Lake Fork (1) | Upper Drift Creek (5) |
| Upper Jackson Creek (1) | Upper Klamath Lake (1) | Upper Lobster Creek (1) |
| Upper Lobster Creek (Alsea River) (1) | Upper Middle Fork Coquille River (1) | Upper North Fork Nehalem River (2) |
| Upper North Fork Siletz River (1) | Upper Olalla (1) | Upper Salmon River (1) |
| Upper Siletz River (3) | Upper Smith River (2) | Upper South Umpqua River (3) |
| Upper Steamboat Creek (1) | Upper Umpqua Indians (1) | Upper Umpqua River (4) |
| Upper West Fork Smith River (1) | Upper Yaquina River (40) | upwelling (16) |
| Uranium (15) | urban development (52) | USSR (1) |
| Utah (7) | | |
