Located only a short distance from the city of Rome, Pozzo del Merro is the world's deepest known flooded karstic cavity, which extends to a depth of at least 400 meters. It opens in one of Italy's Integral Reserves in an area called Macchia del Barco e Macchia di Gattaceca. Pozzo del Merro has been compared with Zacaton, one of Mexico's most famous cenotes; both sites feature dark water and opportunities for free diving champions and scuba diving pioneers alike to create new records, but at just under 400 meters deep, Pozzo del Merro is deeper than the 319 meter deep Zacaton.
Diving Pozzo del Merro: The Pond and the Cave
Situated in an unassuming little parkland, the pond is located at 140 to 150 meters above sea level, looking to all the world like nothing much more than a very large pond or a really small lake - a place no one would really ever think about diving. It is situated in a large sinkhole 120 meters long and 70 meters wide, and with its surface no more than 27 meters across and covered in little aquatic plants called Lemna, it has an appearance similar to any other pond you might find in a natural environment.
Surrounded by steep rocky walls that rise up for about 80 meters, the pond certainly must have been much deeper millions of years ago; once you find yourself beneath the surface, you'll see that the limestone formations continue on into the depths.
Entry is made easy via some stairs carved in the stone surrounding the karst; these were once used by people who came to get fresh water from the pond. In the past, stories circulated about people drowning in unexpected eddies in Pozzo del Merro, and tales that told of their missing bodies being found later in the sea. Currently, there is no proof to substantiate any of these stories especially since the water is pure and fresh.
At first, people guessed that the little pond was 50 meters deep or maybe as deep as 90 meters, an in the late 1990's a group of Italian scientists and cave divers decided to try to find out. During an excursion in the spring of 1999, they reached a depth of 100 meters, and ultimately decided to bring in remote controlled submarines to probe further into the karst. The first sub, Mercurio, reached a depth of 210 meters but was limited by its umbilical and could go no further. The next sub, Hyball 300, reached a depth of 310 meters, and finally, a submarine called Prometeo reached the depth of 392 meters, where the sinkhole stops its vertical descent, leading into an unexplored horizontal passageway.
The karst narrows as you go down; as you make your way deeper, it is only 4 to 5 meters across, and the water is a chilly 16 degrees Celsius. As you descend, there are side passages which can be explored; some are as long as 70 meters. Inside these passages, there are additional shafts leading down vertically; only ROV's have entered them as exploration has been deemed too risky for divers. At its base though, the karst opens up again, and estimates are that the main chamber here is about 30 meters across.
Situated in the Cornicolani Hills, about 23 kilometers from Rome and Vatican City, at the base of the Appenines, Pozzo del Merro is just one of the local Karst formations. Here, you'll find numerous sinkholes and caves, along with travertine mines and the lovely town of Tivoli, with its many springs and gushing waterfalls. With plenty to see topside and beneath the surface, the wonders of Rome and the surrounding area offer much for divers and non-divers alike to marvel at. If you're interested in diving Pozzo del Merro, or any other nearby caves, be sure to contact one of Italy's many capable dive operators to book a trip.