A marine biologist claims to have discovered a huge underwater sinkhole—or blue hole—in the Great Barrier Reef.

Blue holes are large marine sinkholes that mostly formed during past ice ages when sea levels were much lower—meaning they were subject to the same erosion from rain and chemical weathering as any other area. After being submerged, the erosion ceased, and the deep blue caverns were left.

Johnny Gaskell noticed the lagoon using Google and decided to explore the region more closely. Upon visiting the site he discovered a thriving ecosystem, which he described in an Instagram post.

“After spotting this deep blue hole on google maps we decided to head far offshore, out further than our normal Reef trips to see what dwelled within,” he wrote. “At around 15-20m [50-65ft] deep there was huge Birdsnest Corals (Seriatopora) and super elongated Staghorn Corals (Acropora) both of which were among the biggest and most delicate colonies I've ever seen.”

Five months earlier, he said, this part of the Great Barrier Reef was hit by a Category 4 cyclone. The blue hole appeared to be “totally unaffected” by the storm; Gaskell suggests the deep walls of the blue hole appear to have protected the coral.

While it is not clear exactly where the newly discovered hole is, the storm Gaskell is referring to may be Cyclone Debbie, which hit Queensland in March. That cyclone moved over the section of the Great Barrier Reef that sits between Townsville and Mackay, Queensland.

“We may very well be the first to ever dive Gaskell's Blue Hole as it was so far offshore and hidden deep within one of the Great Barrier Reef's biggest lagoons,” said Gaskell.

It is not much of a surprise that such a large feature could exist on the Great Barrier Reef without being discovered earlier. It is the largest structure on Earth to have been created by living organisms and stretches for more than 1,400 miles, covering an area of around 133,000 square miles. Scientists continue to find new species living there.