| River forming the borders of parts of five states | 49 |
| River forming part of the Germany-Netherlands boundary | 54 |
| River forming part of the European-Asian border | 47 |
| River forming part of Germany's eastern border | 50 |
| River formed near Fort Wayne | 28 |
| River formed by the junction of the Fulda and Werra | 51 |
| River formed by the Congaree and Wateree | 40 |
| River formed at Pittsburgh | 26 |
| River formations | 16 |
| River formation | 15 |
| River forest firth | 18 |
| River for the young Moses | 25 |
| River for some boatmen | 22 |
| River for poet Masters | 22 |
| River for Burns | 15 |
| River followed by the Pony Express | 34 |
| River followed by the Oregon Trail | 34 |
| River flowing to the Seine | 26 |
| River flowing to the Rhine | 26 |
| River flowing to the Missouri | 29 |
| River flowing to Rennes | 23 |
| River flowing through Zaragoza | 30 |
| River flowing through Venezuela | 31 |
| River flowing through Kazakhstan | 32 |
| River flowing through Ghent | 27 |
| River flowing into the Severn | 29 |
| River flowing into the Seine | 28 |
| River flowing into the Rhine | 28 |
| River flowing into the Ouse | 27 |
| River flowing into the Oise | 27 |
| River flowing into and out of Lake Geneva | 41 |
| River flowing from France into Germany | 38 |
| River flowing between two Great Lakes | 37 |
| River flowing beneath Paris's Pont Neuf | 43 |
| River flowing alongside Notre Dame | 34 |
| River floater | 13 |
| River float, at times | 21 |
| River fish | 10 |
| River ferried by Charon | 23 |
| River feeding | 13 |
| River feeders | 13 |
| River feeder: Abbr. | 19 |
| River feeder | 12 |
| River fed by the Wabash | 23 |
| River fed by the Porcupine | 26 |
| River features | 14 |
| River featured in Guinness flick | 32 |
| River featured in "The Ten Commandments" | 50 |
| River feature | 13 |
| River famously crossed by Caesar | 32 |
| River facetiously described as "a mile wide at the mouth, but only six inches deep" | 93 |
| River explored by V. L. Cameron et al. | 38 |
| River explored by David Livingstone | 35 |
| River entering the Fulda | 24 |
| River ends? | 11 |
| River ending at the Dead Sea | 28 |
| River ending at Ghent | 21 |
| River encircling Hades | 22 |
| River emptying into Green Bay | 29 |
| River embankments | 17 |
| River embankment | 16 |
| River ducks | 11 |
| River duck | 10 |
| River drops | 11 |
| River drainage area | 19 |
| River down under? | 17 |
| River down under | 16 |
| River dot | 9 |
| River dividing New York City | 28 |
| River dividing Germany and Poland | 33 |
| River dividing Asia and Europe | 30 |
| River deposits | 14 |
| River deposit | 13 |
| River delta, e.g. | 17 |
| River deliberately flooded in W.W. I | 36 |
| River dams | 10 |
| River dam | 9 |
| River curve | 11 |
| River crossing France's Nord department | 43 |
| River crossing | 14 |
| River crosser, perhaps | 22 |
| River crosser | 13 |
| River crossed in the Korean War | 31 |
| River crossed in Joshua | 23 |
| River crossed by the Ponte Vecchio | 34 |
| River crossed by the Pont d'Avignon | 39 |
| River crossed by the North Beacon Bridge | 40 |
| River crossed by the Longfellow Bridge | 38 |
| River crossed by Orpheus | 24 |
| River crossed by Charon | 23 |
| River crossed by Allied forces in February 1945 | 47 |
| River crossed by a ferry in a 1965 top 10 hit | 45 |
| River critters | 14 |
| River critter | 13 |
| River craft: Abbr. | 18 |
| River craft | 11 |
| River conveyance | 16 |
| River connected to a 165-mile long European canal | 49 |
| River connected by canal to the Volga | 37 |
| River connected by canal to the Tiber | 37 |