You were curious to find out what a mermaid's pussy felt like, so you decided to give yourself that chance, and swim closer to Mandy while you were already erect enough to enter her. Mandy swam up to you, and touched your erect penis, as she placed it in her pussy, and you began to have sex underwater, which felt extremely good.
You both spent countless minutes fucking underwater, until you came after penetrating Mandy 50 times. You were worried how this would effect you both, if you became a father. "Don't worry," Mandy says. "Humans can't get mermaids pregnant. Only merman themselves. Come on, let's head back." You follow Mandy back to the beach, where you left your swim-shorts, and beach towels, and of course she was too heavy to carry, when she didn't have legs. To that, Mandy grabbed a towel, and rubbed her legs.