Although there are dangers involved with any type of high diving, even when training in controlled conditions for platform diving, the biggest dangers are associated with jumping into unknown waters from cliffs or other high elevations. When diving from great heights, water doesn't soften your landing. The speeds at which you hit the water make it feel like you are hitting a wall instead of liquid.
One of the biggest threats associated with diving from heights is the speed you build up before you hit the water. In the few seconds you're airborne, you can end up going faster than the local roadway speed limit. For example, if you're jumping from 20 feet above the water, you could be falling at about 25 mph when you hit it. When you dive from around 60 feet, you could be speeding at 60 mph when you touch the water. If your body isn't perfectly positioned, hitting the water at these speeds could cause compression fractures, as well as spinal injuries and concussions.
What You Can't See Can Hurt You
If you're jumping into an outdoor body of water such as the ocean or a river, there's no way to know exactly what's under the water or how deep it is at any given moment. There could be rocks or floating logs, for example. Impact with the water could be devastating to your body, but hitting a solid surface under the water is often deadly. The natural ebb and flow of the water also alters the depth temporarily, so water you think is deep enough might be shallower than you think by the time you dive in.
Risk of Drowning
Even if you aren't hurt seriously when you hit the water, you're likely to become disoriented. The forceful impact combined with the depth you sink after jumping from a height could frighten you, making you want to draw in a breath quickly, which isn't safe when underwater. This could lead to panic, which in turn could lead to potential drowning. If you are injured during the jump, you're even more likely to drown, because it's difficult to swim with broken bones. You won't be able to swim at all if you're unconscious. Depending on your location, it could be difficult for rescue teams to get to you fast enough to save you.
Keeping It Safe
Get proper training before attempting any type of high dive, whether indoors or out. Find a professional trainer to help guide you through the safety protocols, which include proper body positioning. From an indoor high dive platform, many people enter the water hands first, followed by their heads. This isn't the safest position for cliff diving, however. Jump in feet first with your arms tightly by your sides in the pencil dive position. Work on this with your trainer starting at low elevations first; if you don't perfect the technique, your body could angle slightly when jumping from heights. Even the slightest angle can lead to serious injury.