Bolivia and Paraguay close the last 3.5 km of an 88-year border file

Bolivia and Paraguay finished the demarcation of their 755.67-kilometre border on 16 September, after three days of meetings of the joint boundary commission in La Paz. The last open piece was 3.5 kilometres along the Rio Negro, also called the Otuquis, between markers X and XI.

Bolivia's foreign ministry said the two countries had completed the delineation of their entire international boundary, a process carried out over 88 years by technical commissions on both sides. "Finalizing the border consolidates a bilateral relationship based on trust and cooperation between the two states and closes a historical chapter to build a secure and mutually recognized border," the ministry said. Paraguay's foreign ministry said the result would make Bolivia and Paraguay the only two countries in South America to share a fully demarcated border.

The teams used high-precision drone surveys and compared them with desk records. Over 2024 they ran hydrographic and bathymetric studies on the river. In 2025 they fixed 46.5 kilometres of the fluvial course and left the last 3.5 kilometres for the La Paz plenary. Across the wider line they updated coordinates, built 79 second-order markers and cut a border path of more than 700 kilometres. The finished line runs from Hito I, the tripoint with Argentina, to Hito XI, the tripoint with Brazil.

What the Chaco War left behind

Bolivia and Paraguay fought from 1932 to 1935 over the Chaco Boreal, a dry plain both governments thought might hold oil. The war killed between 80,000 and 100,000 people. Bolivia lost a tract larger than half of Paraguay's present territory. A peace and boundary treaty in 1938 started the demarcation. Eighty-eight years is a long time to place stones. Rivers move. Records disagree. Governments change. The last kilometres were the ones where water made the old paper least useful.

A fully marked border does not settle every other dispute two countries may have. It does settle the question of where the line is. For customs posts, road projects and oil and gas blocks that sit near the river, that is the question that matters. Investors and patrols prefer a coordinate to a narrative.

A rare finished file

South America still has stretches of frontier that exist in treaties and not on the ground. Chile and Bolivia remain at odds over access to the Pacific. Venezuela's claim on Essequibo sits over Guyana. Colombia and several neighbours still argue over river mouths. Against that list, a 3.5-kilometre close-out after 88 years is a small act with a large date stamp.

The method is also the story. Drones, bathymetry and a three-day meeting in a capital did what two generations of mixed commissions could not finish. That is not romance. It is what happens when both sides decide the file is worth less as a grievance than as a finished map. The map is now finished. The river will still move. The next commission, if there is one, will be a maintenance body, not a war-inheritance body. That is the change.