The pressure underwater is undeniably strong. If you were to fill a balloon with water and take it underwater, it would not burst but would stay the same size because liquids are not compressed. The pressure is the same, inside and outside of the balloon. If you were to fill that same balloon with air instead, the lower it dives into water, the more it shrinks, until it eventually can't take the pressure anymore and bursts.
A flashlight works on the same principle, and this video tutorial will show you how you can make a waterproof flashlight capable of diving depths of greater than 80 feet. This comes in handy for all you scuba divers taking video and pictures of the depths below. The solution is as spill as adding oil to the flashlight innards. The best part about this underwater flashlight— it's cheap, at under $4 additional cost.