A landscape of dissolved rock
The Corumbá Sinkhole Lakes show the history of a vast subterranean world. Located in the Serra da Bodoquena plateau, this region is one of Brazil's most extensive continuous karst areas, stretching approximately 200 kilometers. The landscape is built from Neoproterozoic-era soluble carbonate rocks, primarily limestone and dolomite.
The formation process begins with rainwater, which becomes slightly acidic as it absorbs carbon dioxide from the atmosphere and soil. This weak carbonic acid reacts with the calcium carbonate in the limestone, slowly dissolving the rock along cracks and fissures. Over millennia, this process carves out extensive underground drainage systems and large caverns. When the roof of one of these subterranean chambers can no longer support the weight above it, it collapses, creating a deep, often circular depression known as a doline, or sinkhole. Many of these then fill with groundwater, forming the region's characteristic clear-water lakes.
The exceptional water clarity, with visibility that can exceed 60 meters, results from two primary hydrogeological processes. First, the groundwater that feeds the lakes is naturally filtered as it percolates through the porous limestone, which removes suspended particles. Second, the water is supersaturated with dissolved calcium carbonate. This mineral precipitates out of the solution as calcite, binding to fine organic particles and pulling them to the lake floor, further cleansing the water column.
Access to an underworld
These sinkholes are not isolated ponds; they rather access points to a complex, interconnected aquifer. They are phreatic caves, formed by the flow of groundwater that dissolved the limestone. This means many lakes that appear separate on the surface are actually connected by a network of submerged conduits and tunnels.
The Abismo Anhumas ("Anhumas Abyss") provides a dramatic example of the scale of these formations. Access to its underground lake requires a controlled 72-meter rappel through a narrow opening in the rock. The lake itself is over 80 meters deep and contains enormous submerged stalagmites, some reaching 20 meters in height. These structures, formed by the slow dripping of mineral-rich water, show that the cave was once dry before the water table rose.
Another famous site, the Lagoa Misteriosa ("Mysterious Lagoon"), is one of Brazil's deepest submerged caves. In 1998, diver Gilberto Menezes de Oliveira reached a depth of 220 meters (720 feet) without finding the bottom. The true depth of the system remains unknown. The water in these lakes is typically oligotrophic, or low in nutrients, which limits the growth of algae and contributes to the remarkable visibility. From approximately October to April, however, rising temperatures can cause algal blooms that reduce clarity, and some sites close to visitors.