| 100% | WABASH | 6 | River that forms part of the Illinois-Indiana border |
| 80% | RHINE | 5 | River that forms part of the France/Germany border |
| 79% | GUADIANA | 8 | River that forms part of the Spain-Portugal border |
| 78% | NIAGARA | 7 | River that forms part of the U.S.-Canada border |
| 78% | ODER | 4 | River that forms part of the border between Germany and Poland |
| 78% | ORINOCO | 7 | River that forms part of the border between Colombia and Venezuela |
| 78% | MOSELLE | 7 | River that forms part of the border between Germany and Luxembourg |
| 78% | DOURO | 5 | River that forms part of the border between Spain and Portugal |
| 78% | RIONEGRO | 8 | River that forms part of the border between Colombia and Venezuela |
| 77% | ELBE | 4 | River that formed part of the border between East and West Germany |
| 74% | DOURO | 5 | River that forms part of the border between Spain and Portugal before flowing west to the Atlantic |
| 69% | DEE | 3 | River that forms part of the England/Wales boundary |
| 69% | YALU | 4 | River that forms a large part of the border between North Korea and China |
| 67% | MAMORE | 6 | River rising in the Andes that forms part of the Bolivia-Brazil border |
| 67% | MEKONG | 6 | River that forms much of the Laos/Thailand border |
| 66% | KASAI | 5 | Tributary of the Congo River that forms part of the border between the Democratic Republic of the Congo and Angola |
| 64% | WABASH | 6 | Part of the Illinois/Indiana border |
| 63% | TAMAR | 5 | River that forms most of the border between Cornwall and Devon |
| 61% | ARAS | 4 | River forming part of the border between Azerbaijan and Iran |
| 61% | MOSELLE | 7 | River forming part of the border between Germany and Luxembourg |
| 60% | PERU | 4 | The Putumayo River forms part of its northern border |
| 58% | IOWA | 4 | The Big Sioux River forms part of its border |
| 57% | BERMEJO | 7 | River of N Argentina forming part of the border with Bolivia |
| 57% | ULNA | 4 | Bone that forms part of the forearm |
| 56% | DEADSEA | 7 | Salty lake that forms part of Jordan's border |
| 56% | URALS | 5 | Mountains that form part of the Asia/Europe boundary |
| 55% | SNAKE | 5 | — River, US watercourse forming part of the border between Idaho and Oregon |
| 55% | MONTE | 5 | Town and resort that forms part of the principality of Monaco |
| 55% | STMARYS | 7 | River that forms the Michigan-Ontario border |
| 54% | IOWA | 4 | The Mississippi and Missouri rivers form parts of its border |