The hidden landscapes of Brazil’s Pantanal

For years, geologists and geographers from Brazil and abroad have been studying the landscapes that shape the floodplain of the Rio Negro, in the southern portion of the Pantanal. Even after all this time, the experts were unaware that under a huge carpet of aquatic plants, there was a huge hidden lake.

In a paper published in October in the scientific journal Earth Surface Processes and Landforms, researchers from São Paulo universities described the discovery of a lake that occupies an area equivalent to a little over two-thirds of the city of São Paulo. “It was almost impossible to identify it at first sight,” said geographer Eder Renato Merino, a researcher at the Institute of Energy and Environment of the University of São Paulo (IEE-USP), one of the authors of the study.

“From a distance, the accumulation of water hyacinths and baceiros along its surface makes it look like an area of land covered by grass.” Water hyacinths—floating aquatic plants of the genus Eichhornia—and baceiros are islands of floating vegetation in the middle of flooded areas.

Mr. Merino is one of those credited with identifying the lake, located in the floodplain of the Rio Negro. The finding was the result of satellite imagery analyses carried out during his Ph.D. course, concluded in 2016 under the guidance of geologist Mario Luis Assine, of the Institute of Geosciences and Exact Sciences of the São Paulo State University (Unesp) in Rio Claro. For decades, he has been studying the transformations that the landscape of the Pantanal—one of the world’s largest floodplains—has undergone. In this case, he and Mr. Merino were interested in investigating the formation of the Rio Negro plains and the process of capturing and distributing water and sediments in the region during the rainy season, between the months of October and May.

Uncovering the lake

During analysis of the course of the Rio Negro, from its sources on the plateau to the lower and flatter lands of the Pantanal, they observed that this body of water spread as it advanced over the floodplain. It changed course and created several winding...