Lisa moaned in a way you'd never heard before. "My legs..." she managed to gasp. "They...feel...so...strange..."
You brought things to a stop. "Are you okay?"
Beneath you, Lisa's legs spasmed, knocking you to one side. You looked to see what might be the problem and were shocked to see her legs were turning pink! It was almost the same shade of pink as the shirt she'd discarded before entering the pond.
"Your legs are changing color. We better get you to a doctor..."
You start to get up to help your girlfriend out of the pond, but your legs go weak and you're unable to stand up.
"I can't get up. I think there's something wrong with my legs too."
"I can't pull my legs apart" says Lisa.
You look over and sure enough your girlfriend's legs seem to be merging into one leg...or is it a tail? An impossible though occurs to you but is confirmed when you look at Lisa's feet. "Your legs are turning into a pink mermaid tail!"
"Look at your legs!" she exclaims.
You do and you realize the reason for the weakness in your legs: your legs are turning into a tail as well. Your tail is a dark shade of blue, similiar to the jeans you were wearing earlier.
Lisa runs her hands down her side, feeling the transistion from her normal skin to pink scales around where her hips used to be. She repeats the motion again and again, gently sliding her hand against the side of her tail. She smiles at you and slides closer to you.
"I think we were in the middle of something..." Lisa says with a sultry tone.
You feel a familiar stirring in a familiar place, but you look down to see only blue scales! What has happened to your manhood? Lisa hasn't noticed something is missing as she gently pushes you onto your back and slides atop you. The feeling of her tail sliding against yours is exhilirating. You've never been so turned on in your life. Lisa presses her lips to yours. Then you feel it sliding out, having apparently been hiding in a slit awaiting just such a moment. Lisa's slit is still in the same place and you enter. You roll the two of you over to put yourself on top again and the passion quickly mounts, reaching heights you'd never experienced before.
After a marathon session, the two of you collapse in the shallows next to each other, exhausted but happy. Light from the full moon bathes the pond as you hold each other close in the afterglow. You begin to wonder about the cause of your new form and whether the two of you will be trapped in the pond.