| 100% | ELBE | 4 | It formed part of East Germany's border |
| 80% | ODER | 4 | It forms part of Germany's eastern border |
| 66% | ELBE | 4 | River that formed part of the border between East and West Germany |
| 61% | ODER | 4 | It forms part of the Polish/German border |
| 59% | ARG | 3 | The Iguazu Riv. forms part of its border |
| 58% | ZIMBABWE | 8 | Victoria Falls forms part of its border |
| 57% | PERU | 4 | The Putumayo River forms part of its northern border |
| 57% | IOWA | 4 | The Big Sioux River forms part of its border |
| 56% | MOSELLE | 7 | River forming part of the border between Germany and Luxembourg |
| 56% | IOWA | 4 | The Mississippi and Missouri rivers form parts of its border |
| 56% | ODER | 4 | River that forms part of the border between Germany and Poland |
| 56% | MOSELLE | 7 | River that forms part of the border between Germany and Luxembourg |
| 53% | RIVERPO | 7 | It forms much of Lombardy's southern border |
| 51% | DEADSEA | 7 | Salty lake that forms part of Jordan's border |
| 49% | NIAGARA | 7 | River that forms part of the U.S.-Canada border |
| 49% | RHINE | 5 | River that forms part of the France/Germany border |
| 49% | HURON | 5 | Lake which forms part of Michigan's northern border |
| 47% | ALABAMABORDER | 13 | The Chattahoochee River forms part of it |
| 47% | ENDPAPER | 8 | Part of it forms the flyleaf |
| 45% | ARAS | 4 | River forming part of the border between Azerbaijan and Iran |
| 45% | ALA | 3 | State where the Chattahoochee R. forms part of the border |
| 45% | EMS | 3 | River forming part of the Germany-Netherlands boundary |
| 45% | ORINOCO | 7 | River that forms part of the border between Colombia and Venezuela |
| 45% | DOURO | 5 | River that forms part of the border between Spain and Portugal |
| 45% | RIONEGRO | 8 | River that forms part of the border between Colombia and Venezuela |
| 44% | SNAKE | 5 | — River, US watercourse forming part of the border between Idaho and Oregon |
| 44% | AFR | 3 | It's east of S.A. |
| 44% | EURASIAN | 8 | Like the Ural Mountains, which form part of the border between two continents |
| 43% | GUADIANA | 8 | River that forms part of the Spain-Portugal border |
| 43% | WABASH | 6 | River that forms part of the Illinois-Indiana border |