Czechs and Slovaks have been exploring the Yucatan underground since 2003, looking for new underground spaces in cenotes, or underwater caves.
The Quintana Roo Speleological Survey has included the new discovery in the list of the longest underwater cave system in the world, it says on its web page.
The Ko'ox Baal system was 36.7 kilometres long. However, its connection, Tux Kupaxa, a smaller, some 20-km-long system, was found last December. Tux Kupaxa became part of Ko'ox Baal then.
The exploration in the cave system continues. It may result in Ko'ox Baal becoming even the world's third longest underwater cave since the Xunaan Ha system, which is over 51 kilometres long is situated some two kilometres from Ko'ox Baal.
If a connection between them is uncovered, it would also become part of Ko'ox Baal. The whole system would be almost 110 kilometres long then.
Moreover, Ko'ox Baal is now the longest underwater cave system that is mapped as well.
"We never abandon any of the newly discovered caves before completing its map. Unfortunately this is an exception in Yucatan," Hutnan said.
Czech speleologists' work helps reveal the mysteries of the prehistoric era. They have found bones of prehistoric animals, extinct long time ago, in the underwater caves. One of them is a rare skeleton of an unknown sloth species.
Czech and Slovak speleologists will present their successes in Mexico at the 16th International Speleological Congress to be held in Brno next year.
The event took place in the then Czechoslovakia only once. It was in Olomouc, north Moravia, in 1973.