We’re pretty focused on science here at Ocean Conservancy, but who doesn’t love a scary story or a creepy mystery on Halloween? Gather around with your closest friends and share these spooky urban legends of the sea—if you dare. From disappearing ship crews to man-eating seaweed and legendary dragons, we’ve rounded up some of the best ocean horror stories to make your Halloween a ‘dolphinately’ frightening one this year.

• Did a sea monster eat a 3 meter Great White Shark?
  • In 2003, scientists tagged a nine-foot Great White in Australia as part of a research study. However, upon checking the tracking device, something eyebrow-raising occurred. The device detected that suddenly, the shark plummeted 1900 feet in a matter of seconds and its body temperature skyrocketed nearly 20 degrees. The only viable explanation, according to researchers? Some sort of massive sea creature must have swallowed it, dragging it deeper into our ocean and turning it into a meal. Yet, what could’ve eaten an animal this huge is still highly debated. Some theories include a ‘monster shark,’ but today, most scientists believe the culprit to have been a sperm whale. They still don’t know for sure, though, so the creature that really lurks below may harbor its secret identity forever. 

• A giant beam of blue light dumbfounds cruise goers
  • In a highly shared story on Reddit, a man described one of the most unexplainable things he’d ever seen. Apparently, in 2012, this individual was on a cruise to Bermuda and was spending some time on one of the decks one night. Suddenly, a large cloud parted in the sky and a giant beam of bright blue light went straight from the cloud all the way to the horizon. No one that saw this phenomenon thought it was a lightning bolt, as for a few seconds, the entire sky was lit up in a bright blue array of color. Neither did they believe it to be a shooting star, since the bolt of light descended in a perfectly straight-edged line. No one on the ship (even the Captain, with experience sailing Bermudian waters) ever did figure out what it was.

• Baltic Sea Anomaly
  • Legend has it that in 2011, the sonar equipment of a diving company called Ocean X detected something strange in a sea bed off the coast of Sweden. Measuring 60 meters thick with evenly placed grooves in the surface, it appeared to be located at the end of some kind of 300 meter long runway. Countless researchers, divers and scientists have proposed their ideas for what the object and its arrangement could actually be, ranging from a battleship gun turret to sediment displaced by fishing trawlers. Many reports today believe the object to be a glacial deposit naturally settling into the obscure form, but we may never know where this anomaly really came from. Which makes it a bit more fun, don’t you think?

• The Mary Celeste
  • In 1872, the Mary Celeste was found off the coast of Portugal, appearing to be “aimlessly” floating along. When those who discovered the curious boat boarded the ship, not a single member of the crew was anywhere to be found. No signs of foul play were present and all of the crew members’ belongings were still intact and undisturbed. The ship’s only lifeboat was the only thing missing and what caused the entire crew to leave the ship behind is a mystery to this day.

• Ghost divers of California (and Grenada)
  • In 2012, a small group of scuba divers exploring the waters off the coast of Santa Monica reported seeing another diver with a pink tank toward the bottom of a blue hole. As they neared the diver, it vanished in front of their eyes. A similar story was told by divers on a diving trip in the Grenadines, who saw another diver in a white shirt waving at them as he swam by. The unsuspecting divers assumed it to be one of the members of their trip, but upon returning to the boat, no one there was wearing a similar white shirt or said they saw a diver of this description.

• 1968 Submarine Disappearances
  • In the late 1960s, four separate submarines—all from different countries—vanished without a trace. Including submersible units from the U.S., France, Israel and the Soviet Union, the disappearances still have yet to be explained. Theories vary, from accidental torpedo attacks kept quiet by the government; even a Navy Court of Inquiry announced that “The cause of the loss cannot be definitively ascertained.” None of the remains of any of the subs have ever been found.

• Man-eating seaweed?
  • According to old folklore, stories of carnivorous seaweed in the Sargasso Sea were responsible for a number of crew disappearances in the 1800s. This body of water is known for its massive accumulations of sargassum, or collectives of a certain type of dense, brown seaweed. A number of empty ships have been found sailing its waters, with the crew members (like that of the Mary Celeste) gone without a trace. There is no evidence of any type of seaweed with such a man-eating quality, so where exactly the details of this urban legend came from has yet to be explained.

• The “Devil’s Sea”
  • Off the coast of Japan lies what has come to be called the Pacific Bermuda Triangle, nicknamed “The Devil’s Sea.” Apparently, ancient legend tells of enormous hidden dragons that lurk in this body of water and the unexplained disappearance of numerous Japanese fishing vessels don’t do much to dispel these stories, either.

Maybe these stories are just whale tales or ancient sea lore. It’s no wonder there are so many mysteries of the deep. While two-thirds of our world is covered by the sea, only about 5% of our ocean waters have been explored thus far, or topographically imaged by oceanographers. If we haven’t discovered what lurks in 95% of our ocean, who can say what species we have yet to discover? On holidays like Halloween, it’s a great opportunity to add a little wonder and mystery to the boundless possibilities of the sea…even if only confirmed as urban legend!