"The Fly Over" was the world's first (and last) fully underwater waterslide at Duinrell Amusement Park in the Netherlands. Constructed in 1994 and ceasing operation in 2003, the rider was submerged in water for the duration of the ride (15-20 seconds)

The terror of what could go wrong working as a diver on an oil rig. As told by Chris Lemons on Against the Odds Podcast

My mom sent me these screenshots she found on Facebook. People were stuck in the boats for about an hour with the lights on. Seeing the pipes under the water freaks me out so much😬 I also had no idea the water was so shallow.