The world's deepest underwater cave is discovered in the Czech Republic by a team of explorers led by a Polish diver, Krzysztof Starnawski.

A Czech-Polish expedition team funded in parts by National Geographic found that the underwater cave, Hranická Propast, is 1,325 feet (404 meters) deep. Hranická Propast is 39 feet deeper than Italy's Pozzo del Merro, the world's second deepest underwater cave. The research team used a remotely operated vehicle (ROV) to explore the bottom of the limestone abyss.

Starnawski first explored Hranická Propast, or Hranice Abyss, in 1999. In 2014, the Polish diver reached a depth of 656 feet, which he first mistook to be the bottom of the cave. However, he discovered a narrow "squeeze passage" that lead to another vertical tunnel. Starnawski then used a probe to explore the pitch-black tunnel further but it ran out of line at the depth of 1,260 feet.

In 2015, Starnawski returned to Hranická Propast and found that the passage had widened, allowing him to enter the tunnel by himself. After reaching a depth of 869 feet he lowered another probe, which landed at 1,214 feet - possibly on debris formed from the passage above.

On Sept. 27, Starnawski and his team finally made the historical discovery with the help of an ROV they released at the depth of 197 feet. From there the team navigated the robot to the bottom of the cave at 1,325 feet.

"I scuba dived down to 200 meters just before the ROV's deployment to put in the new line for the robot to follow," said Starnawski in an interview with National Geographic. "I came back to the surface, and then we went down with the robot to a depth of 60 meters (197 feet). From there, the team at the surface navigated it, via fiber-optic cable, down along my new line to 200 meters deep. Then it went down to explore the uncharted territory - to the record-breaking depth of 404 meters."

When Starnawski was asked why he deployed the robot at 656 feet instead of diving deeper by himself, he noted that his intention wasn't to be called as the deepest diver ever but to aid the ROV in exploration. The motive was to explore the cave beyond 400 meters (1,312 feet), which can't be done by a scuba diver.

Starnawski also noted that the depth gauge used in the process is certified by the state commission and therefore the measurements are absolutely accurate. The diver also added that he spent between two and four hours in the underwater decompression chamber located close to the surface after returning from such a depth.

Photo: Erin Khoo | Flickr

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