Cantera El Terrible

Cantera El Terrible is a flooded basalt quarry located at Salto Grande, about 15 km north of the city of Salto, Uruguay. The quarry was carved out of the ground in 1977 to supply the dark volcanic basalt used in the construction of the Salto Grande hydroelectric dam, a joint Argentine-Uruguayan project that closed the Uruguay River with a concrete dam 852 m long flanked by earth embankments. When construction finished, the excavations were left open, and they filled gradually with water from natural springs and slow seepage from the new Salto Grande reservoir rather than from the river itself. What remained were two distinct pits cut into solid rock: a smaller pit reaching around 6 m deep and a larger one ranging from 12 to 15 m.

The terrain is entirely rock — hard basalt walls with almost no sediment on the bottom, which is why the water stays far clearer than the turbid Uruguay River nearby. Visibility runs 5 to 7 m on a good day, and divers can see the quarry walls rising out of the blue. A Donald Duck statue sits on the floor of the main pit, serving as an orientation landmark and photo subject.

Wildlife in the quarry includes wolf fish (tarariras), armoured catfish, freshwater turtles, sábalos, bogas, mojarras, and dorado. Water temperature swings between about 25 °C in summer and 15 °C in winter, so a wetsuit is recommended year-round.