Few domains exist in the world of diving with as much potential for discovery as the vast underwater cave systems of the Bahamas, North Central Florida and Mexico’s Yucatan Peninsula, which is riddled with underground waterways, accessible only by copious cenotes scattered amidst the jungle. Members of the Czech Speleological Society experienced that thrill of discovery in January, when they connected two previously known systems for the first time, creating the world’s fourth longest underwater cave system. The 12-mile Tux Kupaxa system can now be considered part of the Ko’ox Baal system, increasing the Ko’ox Baal’s official length to 34.35 miles. A little over a mile away, another cave system has been mapped for 32 miles, and if a connection can be discovered, the rankings will again shift, making Ko’ox Baal third.

The Three to Beat

There’s a spiderweb of caves beneath Mexico’s Yucatan peninsula, home to the top three longest underwater systems, as well as Ko’ox Baal — as a point of perspective, Kentucky’s Mammoth Cave — the world’s longest dry cave system — has 390 miles of explored passageways.

1. Ox Bel Ha: 144.9 miles. As of February, 2012, the known length of Ox Bel Ha in the Mexican Yucatan increased from 134.49 miles to nearly 145 miles, giving it a commanding lead as the longest known underwater cave system.

2. Sac Actun: 133.8 miles. Sac Actun actually took the lead from Ox Bel Ha briefly in January 2011 with the discovery that the cave was connected to another, Nohoch Nah Chich.

3. Dos Ojos: 50.89 miles. The Dos Ojos cave system trails behind the top two, but new discoveries link caves every day.