The Pozzo del Merro or Merro Sink Hole is with almost 400 meter deep the deepest flooded sinkhole in the world.

Name Dive Site:	Pozzo del Merro, Merro Sink Hole
Depth:	0-392m (0-1286ft)
Inserted/Added by:	lars, © Author: Lars Hemel
Rated:	Rated 3.7, 3 votes
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The sinkhole Pozzo del Merro (Merro Sink Hole) is Italy's most famous cave, with depths of up to 400 meter, believed to be the deepest flooded cavity in the world, a real geologic and natural monument. It is located 3 km east of Mentana, about 20km north-east of Rome inside the protected nature reserve 'Riserva Macchia del Barco e Macchia di Gattaceca'. It all starts setting up your gear near the entrance of a small 120 times 70 meter large hole in the ground. From there you walk down the stairs to the surface of the 25 meter wide pond some 80 meters below. Dive through the layer of water plants and you can start your dive, first in complete darkness but soon becoming clearer and with higher visibilities. Although fun for recreational scuba divers, it is technical divers with cave specialties that can really explore the sinkhole.

It was not until the late 1990s that scuba divers and scientists decided to find out the actual depth of this world famous sinkhole also called Pozza del Merro or the Merro Well. Up till then, its depth was believed to be 90 meters and there were many tales of people being drowned inside the well. A group of Italian cave divers (Giorgio Caramanna, Riccardo Malatesta and others) decided to put an end to these tales and reached depths of 100 meter in 1999, but as the sinkhole continued going deeper and deeper, they decided to use remote submarines to explore its actual depth. In 2002 a submarine called Mercurio reached 210m but couldn't go any deeper because it ran out of enough connection cable. Other submarines such as the Hyball 300 made it up to 310 meters deep and the Prometeo up to 392. Besides the already narrow and skewed passages, Prometeo couldn't continue because the passage continued horizontally. Future explorations have to find out if the Pozzo del Merro is even deeper.

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