Every year between July and August, something extraordinary happens on a remote stretch of the Guaporé River along the border between Brazil and Bolivia. Tens of thousands of giant turtles emerge from the water and crawl onto the sandy riverbanks to nest — the largest gathering of any turtle species ever recorded anywhere on Earth.
Until recently, nobody knew exactly how large this gathering was. The river is remote, the turtles nest in dense clusters, and traditional ground-based counting methods were inadequate for the scale of what was happening. Then researchers from the University of Florida and the Wildlife Conservation Society equipped themselves with drones and statistical models — and discovered something extraordinary.
41,000 Nesting Females
The study, published in 2025 and widely reported through early 2026, found more than 41,000 nesting female giant South American river turtles (Podocnemis expansa) at the Guaporé site in a single season. That's not just a record for this species — it's the largest recorded aggregation of any chelonian (turtle or tortoise) species anywhere in the world.
The drone survey approach allowed researchers to count individual turtles across stretches of riverbank that were previously impossible to survey comprehensively. Statistical models accounted for turtles missed due to vegetation cover or timing of surveys. The result was a figure that stunned even seasoned herpetologists.
A Species That Has Survived the Worst
The giant South American river turtle, also known as the Arrau or tartaruga-da-amazônia in Brazil, is one of the world's largest freshwater turtles, reaching shell lengths of nearly 90cm and weights of up to 90kg. Females can live for decades and lay hundreds of eggs each year.
The species was historically hunted intensively — for eggs, for meat, and for oil rendered from the fat. Populations collapsed across much of their range in the 19th and 20th centuries. The fact that such a large aggregation still exists on the Guaporé is a testament to the relative protection this stretch of river has received, and to the resilience of the species itself.
Conservation organisations have used the discovery to argue for stronger protections along the Guaporé corridor. The river forms part of the boundary of the Guaporé Biological Reserve in Brazil, but enforcement remains challenging in this remote region.
The World's Biggest Maternity Ward
The nesting site has been described — with some justification — as the world's biggest maternity ward. Each female arrives, excavates a nest in the warm sand, lays between 70 and 150 eggs, and returns to the river within days. The eggs incubate for about 45 days, and the hatchlings emerge in synchronised waves that briefly turn the riverbank into a sea of small dark shapes, all scrambling toward the water.
Many won't survive — predation rates on hatchlings are high. But the sheer scale of this aggregation means that even a low survival rate produces tens of thousands of new turtles each season. It is, in the truest sense, life at scale.
Sources: University of Florida · Wildlife Conservation Society · Mongabay · Popular Science · Discover Wildlife, 2025-2026
