Gruta do Lago Azul
Monumento Natural da Gruta do Lago Azul
Interesting facts
- A tiny blind crustacean from the lake, Potiicoara brasiliensis, was just the second living species ever discovered in its entire order, Spelaeogriphacea.
- The only species of that order known before it lives in a cave on Table Mountain in South Africa, across the Atlantic.
- Researchers later found the same crustacean in caves near Corumbá and in the Araras mountains, extending its known range by more than 700 km.
- Beyond sabre-toothed cats and giant sloths, the Ice Age bones from the lake floor include armadillos, llamas and primitive horses about 12,000 years old.
- The cave chamber measures about 143 metres in length and 80 metres in width, and its lake has been estimated at about 90 metres deep.
- The main chamber needs no artificial lighting: the wide entrance alone lets in enough daylight to see the formations and the water.
- Sensors in the cave log temperature and humidity every 30 minutes, because the body heat of just a few visitors can warm parts of it by up to 3 °C.
- The protected natural monument around the two caves covers about 260 hectares of forest and limestone hills.
Why it is worth it
Gruta do Lago Azul, the Blue Lake Cave, opens in the limestone hills outside Bonito in Brazil's Mato Grosso do Sul as a wide mouth in the forest, about 40 metres across. A path of roughly 300 steps leads down a steep, sloping chamber hung with stalactites to the cave's prize at the bottom: a still underground lake more than 50 metres long whose water is a blue so saturated that it looks lit from within.
That colour is the reason to come. The water is exceptionally clear, and when sunlight falls through the entrance and reaches the lake, the blue deepens to an almost electric tone. This happens most strongly between September and February, when the sun's angle sends a direct beam into the chamber in the morning. The lake's true depth has never been settled: cave divers have descended to about 96 metres without finding the bottom.
The cave is said to have been found in 1924 by a member of the Terena, an Indigenous people of the region. Its depths turned out to be a time capsule. In 1992 a Franco-Brazilian diving expedition recovered bones of Pleistocene megafauna from the lake floor, including a sabre-toothed cat and giant ground sloth, animals that roamed the region at the end of the last Ice Age. The water also shelters a tiny endemic crustacean, Potiicoara brasiliensis, described in 1987. A second cave nearby, Nossa Senhora Aparecida, holds a single great hall about 100 metres wide but stays closed to visitors.
Brazil's heritage institute IPHAN listed both caves as natural monuments in 1978, and visits are tightly managed: small groups go down with local guides, numbers are limited each day, and bookings are made in advance through Bonito's tour operators. Swimming is not allowed — the lake is for looking at.
Getting there
The cave lies about 20 km from the centre of Bonito by road; transport is arranged with a tour agency or by car. Bonito Airport (BYO), about 13 km from town, has scheduled flights from Campinas (Viracopos). The alternative is Campo Grande International Airport (CGR), roughly 290 km away by road.
Plan your visit
We have no confirmed visit data yet. Once it is confirmed, this block also carries the date it was checked.
Nearby places
- Abismo Anhumas 1.2 km · cave
On these lists
From the encyclopaedia
Gruta do Lago Azul Natural Monument is a natural monument in Bonito, Mato Grosso do Sul, Brazil. It holds two caves with interesting but fragile calcareous formations, and has been listed as a protected area since 1978.
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