Starnawski, 48, determined Tuesday that the flooded limestone Hranicka Propast, or Hranice Abyss, which divers have explored for decades, was at least 404 meters deep. He scuba dived to a narrow slot at 200 meters' depth and let through a remotely operated underwater robot, or ROV, that went to the depth of 404 meters, or the length of its cord, but still did not seem to hit the bottom.
In 2015, Starnawski himself passed through the slot and went to 265 meters' depth without reaching the cave's bottom. After diving that far down, Starnawski had to spend over six hours in a decompression chamber. To explore the cave further, he needed a robot.
Speaking on the phone from his home in Krakow, southern Poland, Starnawski said Tuesday's discovery makes Hranice Abyss the world's deepest known underwater cave, beating the previous record-holder, a flooded sinkhole in Italy called Pozzo del Merro, by 12 meters (39 feet.)
Diving in the cave is a challenge because of muddy areas and a water temperature of 15 degrees Celsius (59 degrees Fahrenheit.) The water's mineral composition also damages equipment and hurts any exposed skin, Starnawski said.
