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| Fairdale (Or.) (3) | Fairview Creek (3) | Fairy Creek (3) |
| Falcon Creek (3) | Fall Cr. (1) | Fall Creek (42) |
| Fall Creek (Alsea) (5) | Fall Creek (Siletz) (4) | Fall Creek (Wilson) (1) |
| Fall Creek Fish Hatchery (Alsea River) (1) | Fall Creek Hatchery (4) | Fall Creek Hatchery (Alsea) (2) |
| Falls Creek (1) | Fankport (1) | Fanno Creek (1) |
| Fanno Creek Lake (1) | Farlowa mollis (1) | farming (1) |
| fat gaper = Tresus capax (1) | fat gaper clam = Tresus capax (10) | fat gaper=Tresus capax (29) |
| Fate Creek (3) | Faults (135) | Fauna (13) |
| Fawn Creek (1) | Feagles Cree (1) | Feagles Creek (10) |
| feathery shipworm=Bankia setacea (1) | fecundity (95) | feeding behavior (94) |
| Feldspar (4) | Felton Creek (1) | Fendall Creek (1) |
| Fenton Creek (4) | ferries (4) | Ferry Creek (Coquille) (1) |
| fertilizers (2) | Field Creek (2) | Field guide (3) |
| fill (11) | filling (2) | filtration (1) |
| Fischer Creek (1) | fish (30) | Fish Creek (12) |
| Fish Creek Dam (1) | Fish Creek Forebay (1) | Fish Creek Screen Ponds (1) |
| fish disease (32) | fish diseases (4) | Fish Lake (3) |
| Fish Lake Creek (1) | fish passage (8) | fish screens (1) |
| Fishawk Creek (1) | Fisher (Or.) (3) | Fisher Creek (1) |
| Fisher Formation (1) | fisheries (7) | fishes (250) |
| Fishhawk #2 (2) | fishing (3) | Fishing Hole (1) |
| fishways (2) | Five Mile Point (1) | Five River Boat Launch (1) |
| Five Rivers (56) | Five Rivers (Alsea) (10) | Flat Creek (1) |
| Flat Rock Branch (2) | Flat Rock Creek (2) | flat-tip piddock = Penitella penita (1) |
| flat-tip piddock=Penitella penita (5) | flatworms (1) | Flesher Slough (9) |
| flooding (195) | floods (10) | Flora (3) |
| Floras (1) | Floras Creek (12) | Floras Lake (13) |
| Floras River (1) | Florence (Or.) (9) | Florence dune sheet (3) |
| Florence, Or. (1) | Florida (4) | Florida Keys (1) |
| flouride (3) | Flournoy Formation (3) | fluffy sculpin=Oligocottus snyderi (1) |
| Fluminicola umpquaensis = Jade pebblesnail (1) | Fluminicola fresti = Frest’s pebblesnail (1) | fluoranthene (6) |
| flushing (1) | Flynn Cree (1) | Flynn Creek (73) |
| Flysch (12) | Flysch deposits (3) | Fogarty Creek (7) |
| Fogarty Creek State Park (3) | food availability (14) | Food conditions (1) |
| food sources (1) | Foothill yellow-legged frog = Rana boylii (4) | foothill yellow-legged frog=Rana boylii (1) |
| Footlog Creek (1) | foraminerifera (1) | foraminifera (93) |
| forest fires (50) | forestry (14) | Forks (1) |
| Fort Umpqua (4) | Fortune Branch (1) | Fortune Branch Creek (2) |
| Fortune Branch Creek (Cow Creek) (1) | Foss (Or.) (4) | Fossil Point (2) |
| fossils (111) | Foster Creek (3) | Fouling (1) |
| Fourth of July Creek (1) | Fowler Creek (2) | Fox Creek (2) |
| Fracture zones (3) | France (4) | Frances Creek (1) |
| Francis Creek (6) | Franciscan Formation (1) | Frank and Jeanne Moore Steelhead Sanctuary (1) |
| Franklin Creek (4) | Franklin Creek (Umpqua River). (1) | Franklin's gull=Larus pipixcan (1) |
| Frantz Creek (2) | Fraser Canyon Creek (2) | Fraser River estuary (1) |
| Frazer Creek (1) | Fred Wahl Marine: Scholfield Slough (1) | Freezeout Creek (1) |
| French Creek (3) | freshwater mammals (2) | freshwater mammals (1) |
| Freshwater peal mussel = Margaritifera margaritifera (2) | Freshwater pearl mussel = Margaritifera margaritifera (3) | Frio Formation (1) |
| frogs (1) | Frozen Creek (3) | Frozen Creek (South Umpqua) (5) |
| Fucus species (12) | Fucus spp. (2) | Fuel (1) |
| Fun River (2) | fungi (4) | fungicides (1) |
