Abismo Anhumas

A partly flooded limestone cave about 23 km from Bonito, entered only through a 72 m vertical shaft. Its clear lake, which the operator gives as about 80 m deep, holds limestone cones up to about 20 m tall and is visited by snorkellers and scuba divers.

Abismo Anhumas is a limestone cave in the Serra da Bodoquena karst, about 23 km from the town of Bonito in Mato Grosso do Sul. Its only entrance is a narrow opening at the top of a 72 m shaft, roughly the height of a 26-storey building. At the bottom lies a lake of very clear water; the operator puts its depth at about 80 m, varying with the rainy and dry seasons, and its volume at around 24,000 cubic metres.

Visitors are lowered and raised by an electric rappel system run by the operator, two people at a time, to a floating deck on the lake. From there they can look at the formations, snorkel, or take one of two scuba options. Under the surface, cones of limestone up to about 20 m high rise from the floor; the operator describes the area as a city of submerged cones and also points divers to the skeleton of an anteater that fell into the cave years ago.

The diving offered is lake diving under the entrance shaft rather than cave penetration: an introductory dive to 8 m for people without certification, and a dive for certified divers. The operator's own pages give 18 m in some places and 20 m in others as the limit for certified divers, so check the current limit when booking.

According to the operator, the cave was found by chance in 1970 after a forest fire on the former Fazenda Anhumas, opened to visitors in 1995 and has been under its present management since 1999. No published survey or scientific study of the lake was found for this record, so depth and formation figures are the operator's.

The cave is formed in limestone. The submerged cones and the stalactites and stalagmites above water are calcium carbonate deposits; the operator says the cones reach about 20 m in height and claims the cave holds the largest such cone recorded in the literature, a claim not checked against any published study.

The lake is still water at the foot of the shaft. The operator states that its depth changes with the rainy and dry seasons, reaching about 80 m, that visibility can reach 60 m and that the average water temperature is 18 °C.

Abismo Anhumas is one of the few places in Brazil where non-specialist divers can dive inside a cave lake, and its submerged cones are its main draw. The operator says specialists, including environmental engineers and biologists, inspect the cave every year to check that tourism is not harming it.

The operator gives an average water temperature of 18 °C and visibility of up to 60 m; lake depth varies with the rainy and dry seasons. Sunlight reaches the lake only for a short part of the day. A 2021 PADI blog post suggested December to March as the best period; treat all of this as typical, not current, conditions.

Phạm vi thông thường từ các nguồn đã công bố, không phải điều kiện hiện tại.

One documented entrance: a narrow opening at the top of a 72 m shaft. Access is only by the operator's electric rappel system with the operator's equipment.