Powerful 100m Diving Blue Laser Pointer (100mW / 300mW / 1600mW)

I tried using it 30-50 meters underwater, and it ran for 30 minutes straight with no issues. The waterproofing is better than I expected, and you don't have to worry about overheating. The only downside is that the laser beam is thick, so it's not ideal for long-distance pointing.

This is truly waterproof — no problem even 100 meters underwater! I recommend choosing the 2W version because it has a thick blue beam, and visibility is not enough if the power is too low.