Gruta Azul (Cocalinho)

In 2004, a cave diver found an apparently complete human skeleton in the aphotic zone of Gruta Azul, in a conduit west of the lake. In the most complete human skeleton in the cave, the limb bones have swapped places, which led to the hypothesis of a ritual secondary burial. Dating indicates human presence in two periods: the first more than 10,000 years ago, in an area of the cave estimated to have been submerged for at least 5,000 years, and the second starting about 2,000 years ago.

Since 2020, a group of cave divers has been exploring and mapping the submerged passages, with 1,080 m surveyed by the time of publication. On the 2022 expedition, the team recovered and documented around 400 bones, which were taken to São Paulo for study. In 2025, it recovered a nearly complete skeleton of a tapir species that went extinct over 8,000 years ago and found, in a collapsed part of the cave, human bones mixed with giant sloth and sabre-toothed tiger bones. A complete ceramic jar was also found in the aphotic zone.

The archaeological site was registered as Gruta dos Fósseis because there are many other sites named Gruta Azul in Brazil. There are speleothems in the flooded galleries as well, a sign that the water level was once much lower. Between the rainy and dry seasons of 2021, the lake level varied by 1.8 m.