You struggle as the mermaid notices your penis sticking up from when you were looking at her breasts, and begins to suck on it. Your lungs were starting to fill with water as you struggle to hold your breath. With your penis sticking up, the mermaid starts sucking, and sucking, until eventually a stream of cum jets out.
You manage to get out of the sex, while at the same time, feel something grow on your neck. If that wasn't bad enough, you could feel your own penis begin to shrink, while you continue to paddle. By the time you finally reach the shore, you pass out, and take a nap from doing it so much. However, what changed when you got out of the water is that you no longer had a penis, and gills were now on your neck. A lifeguard notices you come out of the water, as she calls the hospital for you.