I first knew something was wrong when the divemaster gave the briefing. We were minutes from the dock in Cozumel, Mexico, on a dive boat I’d booked through my cruise operator. Our guide looked down at his feet. They were submerged to his ankles. Panicking, he yelled at us to head for the bow, to counterbalance a stern filling with water. The water rose to his knees 10 seconds later. Changing tactics, he shouted again: “Take your weights from your BC and throw them overboard!” We did, but we knew it was too late. This boat was sinking.

More stories from the deep.

Screams erupted from the bow. ­Several couples were standing in the V-berth, where water was flooding in, pushing them farther inside the boat as they fought to get out. Seeing the ­people struggling to exit an overhead ­environment, instinct took over. I jumped ­overboard. I couldn’t believe what was happening. I’ve been a scuba diver for 12 years, and never had I seen anything like this. Over the years, I’d read ­stories of dangers like this, but I didn’t believe them. It just didn’t seem possible. I had booked this shore excursion through the cruise because I believed it would be ­safer. I thought cruise companies vetted dive operators, ensuring the safety of the boats and equipment. I was wrong.

As I treaded water, the boat sank ­completely. All of us, passengers and crew, were now swimming. It all ­happened so fast — less than a minute — that we failed to grab life jackets.

Luckily, when he realized what was happening, the boat captain had radioed a sister ship. We were “stranded at sea” for less than two minutes before help arrived. After a hassle trying to reboard the cruise ship without our ID or ship cards, all of which had sunk, we were able to ­rejoin our families. Moving forward, ­regardless of what cruise company I travel with in the future, I will invest the time to research dive operators and make my own bookings. My biggest requirement: being sure that the boat I depart the dock on is the one that brings me back.