At the southern edge of Colombia, the river that sustains life and commerce is slipping away. The Amazon’s primary current is migrating toward Peru, threatening Leticia’s future, unsettling century-old treaties, and turning a sandbar dispute into a test of sovereignty itself.
An island dispute on a moving river
Santa Rosa barely breaks the surface—a low island clustered with homes and market stalls, pressed against the Peruvian bank at the Amazon tri-border with Brazil. To Lima, it is an appendage of its Chinería island. To Bogotá, it should be Colombian.
On paper, it looks like a familiar boundary quarrel. But the trouble runs deeper than cartography. A century ago, when Colombia and Peru fixed their frontier, Santa Rosa did not exist. The line followed the river’s thalweg—its deepest navigable channel—on the assumption that the Amazon was stable. It was not.
Sediment and current have since birthed new islets and sandbars. More critically, the river itself has been drifting, forsaking Colombia’s channels and pressing harder against Peru. The dispute over Santa Rosa is less about who owns an island than about whether the very water that defines the border can be trusted to stay put. For Leticia, Colombia’s river capital, that uncertainty now feels like a direct threat.
A living frontier, measured in cubic meters
Warnings came decades ago. Studies in the 1990s estimated that 70 percent of the Amazon’s flow at this frontier already ran through Peru, leaving just 30 percent to Colombia. Navy projections later suggested the current could bypass Leticia altogether by 2030.
Fresh measurements suggest the tipping point is near. On June 25, at the Nazareth narrows—the choke point that sets the effective frontier—engineer Juan Gabriel León of the National University of Colombia recorded 55,900 cubic meters of water per second thundering downstream, equal to twenty-two Olympic pools every second. Yet less than a fifth of that—just 10,900 cubic meters per second—was coursing past Colombia’s side.
“The Colombian share has fallen to 19.5%,” León told EFE. “And we were in high water. In September or October, in the dry months, practically no water will likely pass on the Leticia side.”
That means even in a flood, Peru commands the river’s muscle. In drought, Leticia may gaze out at little more than a stagnant reach, its boats stranded, its commerce paralyzed. The Amazon is not just shifting. It is abandoning one side for the other.
Sediment, erosion, and the river’s preference
The Amazon’s betrayal is not arbitrary. It is geomorphology—the science of how land and water reshape each other. Here, the river is “anastomosed,” in Professor Lilian del Socorro Posada’s words: splitting into multiple channels that rejoin downstream, braiding around islands and bars of freshly dropped sediment.
Water quickens in narrow cuts, slackens where the bed widens. The Andean silt it carries settles where the current loses strength. Downstream of Nazareth, León explained to EFE, the river spreads, weakens, and dumps its load. Those deposits clog Colombia’s channels, starving them, while Peru’s arm scours deeper.
The banks themselves differ. Peru’s margin is a soft floodplain, prone to erosion. Clay-rich terraces reinforce Colombia’s. “The river prefers the Peruvian arm because of how that floodplain is built, and so it pulls to that side,” Posada said.
Two decades ago, after exhaustive fieldwork, Posada laid out a fix: dredge between Peru’s Chinería and Colombia’s Ronda islands to clear sediment, and install submerged groynes in Peru’s channel to redirect part of the flow. Technically feasible, financially possible. Politically, ignored. “Governments have turned their backs on rivers,” she says now. And as climate change tightens droughts, the imbalance will only sharpen.
EFE/ WWF Colombia
Leticia’s future and the politics of water
For Leticia, the danger is existential. “Leticia cannot lose its river,” León told EFE. “Commercially, politically, socially, all communities depend on it.” Yet the city is ironically beautifying its waterfront promenade while the Amazon itself slips away.
If the current trend of abandonment continues in Colombia, trade routes will collapse. River transport dries up. Fisheries that feed households vanish. The Yahuarcaca lake system—a biodiverse web just beyond the city—depends on seasonal Amazon floods. Without those pulses, it’s fish, birds, and aquatic plants could die back, unraveling ecosystems and traditions of Indigenous and riverine families who have lived by those waters for generations.
The politics are just as fraught. Because the frontier was anchored to the Amazon’s thalweg, every shift in sediment subtly unravels the old treaty logic. Each sandbar that rises, each channel that clogs, questions whether the border drawn a century ago still means what it did.
The specialists are blunt: louder rhetoric will not hold the river in place. Only renewed binational cooperation can. That means dusting off past studies, funding dredging, building structures to balance the flow, and admitting that the Amazon itself—not speeches or maps—will decide if Leticia remains a river city.
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“Not acting,” Posada warns, “is negligence.”
The flare-up over Santa Rosa has forced Colombia and Peru to confront the unromantic truth: the Amazon’s most significant power is not just the water it carries but the maps it rearranges. Managing that force is no longer optional. It is the only way to keep a city and a frontier afloat.