| PUTUMAYO | River forming most of the border of Colombia with Peru also known as the Rio Ica |
| PILCOMAYO | Chief western tributary of the Paraguay River, forming most of the border between Paraguay and Argentina (9) |
| TAMAR | River forming most of the border between Cornwall and Devon, England (3) |
| PUERTORICO | Somehow Peru also takes in briefly rich island (6,4) |
| NYASA | Third-largest and second-deepest lake of Africa, forming most of the eastern border of Malawi with Tanzania and Mozambique (5) |
| STOUR | River of East Anglia forming most of the county boundary between Suffolk and Essex (5) |
| YALU | River of eastern Asia forming most of the natural boundary between China and North Korea (4) |
| LETICIA | Colombian town where the borders of Colombia, Brazil, and Peru meet (7) |
| ACRE | Unit of land equal to 4,840 square yards; or, a Brazilian state on the border with Peru, capital Rio |
| LAPAZ | Capital and largest city of Bolivia, in the west near the border with Peru (2,3) |
| SPEECHTHERAPIST | ICA thesp suffering with herpes with little time to see with little time to see diction specialist (6,9) |
| ORINOCO | What river is a border of Colombia and Venezuela? (7) |
| ARAL | Inland sea that forms part of the border of Kazakhstan |
| ODER | Part of the border of Brandenburg |
| RHINE | Part of the border of France and Germany |
| SUNSETBOULEVARD | It forms part of the border of UCLA's Westwood campus |
| MOSS | Plant forming most of my lawn! (4) |
| SPLINTS | Supports forming most of base in ship (7) |
| IRAQ | Country forming most of ancient Mesopotamia (4) |
| ARICA | Port in N Chile near the border with Peru (5) |
