Be Ready. Be Covered. Be Sure.

Although it offers a look into a beautiful underwater world, scuba diving can be very dangerous if you're not careful. Often the worst scuba accidents are the result of inexperienced divers making tiny mistakes. While diving, you always have to be alert and conscious of your surroundings. If something does go wrong, panic on your part is the worst response.

At this point, remaining calm might not be enough. Some of the divers who perished on this list were incredibly experienced and well-prepared, but still, couldn't do anything to prevent their own deaths. Listed below are some of the gravest cave diving accidents and wreck diving accidents that have occurred in recent history. If this list teaches you anything, it's to never take scuba diving lightly.

1. Diver Spends 10 Hours in Darkness with Dead Friend 900 Feet Under Water

Friends Don Shirley and Dave Shaw went diving almost 1,000 feet underwater in Bushman's Cave in South Africa when seeking to recover the remains of Deon Dreyer, who had died in the cave a decade before. More people have walked on the moon than have descended to such depths.

Video recovered later revealed that Shaw lost his light in depths and became entangled in the lines he planned to using to hoist Dreyer's body.

2.  Eight Divers Have Perished in Jacob's Well Due to False Exits and Blinding Sludge

Jacob's Well, a beautiful diving spot in Texas has developed a reputation as one of the most dangerous places to dive in the country. Although alluring, at least eight divers have lost their lives in Jacob's Well, with possibly the cruelest being young Richard Patton. The Southwest Texas State University student was looking for a way to move from chamber to chamber in the cave, and ended up getting stuck in a false chimney that looked like a way out.

In parts of this underwater cave system, the floors are covered in fine gravel or silt and if a flipper so much as brushes the surface, the stirred-up sediment fully obscures a diver's vision, essentially blinding them.

3. Diver Panics and Succumbs to Nitrogen Narcosis, Removing His Own Breathing Apparatus

In April 2000, Russian diver Yuri Lipski geared up to dive at one of the world's most beautiful diving spots, the Blue Hole. Located on the east coast of Egypt's Sinai Peninsula, the spot has become a must for divers who want to see the coral-lined, 394-foot-deep sinkhole.

Lipski ended up dying at around the 300-foot mark. When you go that deep, your body is often subjected to nitrogen narcosis, a mental state that starts off similar to extreme drunkenness but can eventually cause severe mental symptoms like hallucinations, paranoia, confusion, vertigo, and eventually death. Experienced Diver Disappears in a Wrecked Ship.

4. An Experienced Diver Vanishes in a Wrecked Ship

No matter how much experience you have diving, one small mistake or error can lead to your death. Diver Tom Pritchard was working on attaching a mooring line to the famed wreck of the Andrea Doria, which had come loose when he suddenly vanished. Pritchard had close to 1,000 dives under his belt and the divers working with him had said Pritchard had a reputation for being incredibly careful and detail-oriented when it came to his dives.

No matter how much experience you have diving, one small mistake or error can lead to your death.

When the other divers surfaced, they immediately noticed Pritchard was not with them.  The Andrea Doria wreckage has always been dangerous and has claimed more than 15 lives due to its unstable nature. As his remains still haven't been found, we might never know whether Pritchard died from equipment failure, a medical emergency, or if some part of the ship simply collapsed around him.

5. A Dive Group Gets Separated from Instructor, Spends 28 Hours Floating in Open Water

While on a tour in Bali, Indonesia, a group of seven people were separated from their boat while out diving. Bad weather was to blame, and the two instructors and five Japanese women floated in open water for 28 hours before eventually reaching a rocky islet where they were rescued two days later. During that harrowing ordeal, one of the women died, with her body being found 30 kilometers from the islet, while one of the instructors went missing in the open water.

It was then discovered the company that took the group out on their dive was operating with an expired permit.

6. Two Divers Perish During Dangerous Dive, Friends Go Back to Retrieve Their Bodies

In Norway, five friends embarked on a dangerous mission to explore a deep cave system in Norway. Going past the 100-meter mark, one of the divers got stuck in a passage and signaled for help. His friend in front of him turned back and did everything he could, but horrifically had to watch his friend die in front of his eyes. The accident caused another diver to panic - which is the worst thing you can do while diving - and he died, too.

After the survivors made it back, the authorities deemed a retrieval mission for the dead bodies to be too dangerous. But that didn't stop the original divers from planning a secret, extensive rescue mission, and seven weeks later, they went back into the dangerous cave system and successfully retrieved their fallen friends.