Zacatón

Zacatón (El Zacatón sinkhole) is a thermal water filled sinkhole belonging to the Zacatón system - a group of unusual karst features located in Aldama Municipality near the Sierra de Tamaulipas in the northeastern state of Tamaulipas, Mexico. It is the deepest known water-filled sinkhole in the world with a total depth of 339 metres (1,112 ft): the 392 metres (1,286 ft) plus deep Pozzo del Merro (Sant'Angelo Romano, Latium Region, Italy) is deeper (actual depth yet unknown), but its nature as a near-vertical cave or a sinkhole still being debated.