| 100% | WESER | 5 | River formed by the junction of the Fulda and Werra |
| 61% | YAZOO | 5 | River in Mississippi, US, formed by the confluence of the Tallahatchie and Yalobusha Rivers |
| 61% | SHATTALARAB | 11 | River in SE Iraq formed by the confluence of the Tigris and Euphrates Rivers |
| 58% | GIRONDE | 7 | Estuary in France formed by the confluence of the Rivers Dordogne and Garonne |
| 51% | SANTEE | 6 | River formed by the Congaree and Wateree |
| 49% | PARANA | 6 | River of South America formed at the confluence of the Paranaiba and Grande Rivers in Brazil |
| 48% | OPAL | 4 | "Steven Universe" character formed by the fusion of Amethyst and Pearl |
| 48% | OFGEM | 5 | Non-ministerial government department formed by the merger of OFFER and Ofgas |
| 48% | ARAS | 4 | River forming part of the border between Azerbaijan and Iran |
| 48% | URAL | 4 | River forming part of the boundary between Europe and Asia |
| 48% | MOSELLE | 7 | River forming part of the border between Germany and Luxembourg |
| 47% | DOUBLE | 6 | With 52-Down, betrayal, and what's formed by each pair of the trigrams |
| 46% | THUN | 4 | Lake —, body of water in central Switzerland formed by a widening of the Aare River |
| 46% | UNISON | 6 | Trade union formed in 1993 by the amalgamation of COHSE, NALGO, and NUPE |
| 46% | LAUNDRYLIST | 11 | Extensive enumeration ... or what's formed by the ends of 17-, 23-, 34- and 48-Across |
| 46% | YALU | 4 | River that forms a large part of the border between North Korea and China |
| 45% | IOWA | 4 | The Mississippi and Missouri rivers form parts of its border |
| 45% | HUMBER | 6 | Large tidal estuary in northern England formed by the Rivers Ouse and Trent |
| 45% | ODER | 4 | River that forms part of the border between Germany and Poland |
| 45% | TAMAR | 5 | River that forms most of the border between Cornwall and Devon |
| 45% | ORINOCO | 7 | River that forms part of the border between Colombia and Venezuela |
| 45% | MOSELLE | 7 | River that forms part of the border between Germany and Luxembourg |
| 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% | ELBE | 4 | River that formed part of the border between East and West Germany |
| 44% | INDUS | 5 | River fed by the snows of the Himalayas |
| 44% | MEAD | 4 | Lake —, reservoir in Arizona and Nevada formed by the Hoover Dam across the Colorado River |
| 44% | SNAKE | 5 | — River, US watercourse forming part of the border between Idaho and Oregon |
| 44% | MEAD | 4 | Lake —, reservoir in Arizona and Nevada, US, formed by the Hoover Dam across the Colorado River |
| 43% | RHYMNEY | 7 | River in Wales forming the boundary between the historic counties of Glamorgan and Monmouthshire |