You get an idea and go back to the bedroom where your girlfriend is still relaxing on the bed.
"Hey Lisa, there's a little lake out back like the ad said and there's no other cabins on it or anything. We've got it all to ourselves."
She sits up on the bed. "All to ourselves? Nobody to see us at all?". She gets a mischevious grin on her face and you're sure she knows what you have in mind. The two of you head out the back door of the cabin.
You walk part way around the pond, holding Lisa close the whole way. The water is clear and clean and doesn't look too deep. Your initial conclusion is confirmed: just forest around the pond, no sign of even a trail leading away from it.
Lisa suddenly turns to you and says with a smile "I think this looks like a good place."
She pulls away from you and takes a step toward the water. She pulls off her shoes and socks before slowly pulling her pink shirt over her head then droping it on the ground. She slowly wriggles her pants down her legs, leaving them on the ground by her shirt. She slowly unhooks her bra, but teasingly turns away at the last moment. It and her panties join the rest of her clothing on the ground. She walks slowly and seductively into the water, giving you a great view of her perfect butt. As she wades in she looks back and motions with one finger for you to join her.
Skinnydipping is of course what you had in mind all along. You quickly remove your clothing and follow Lisa into the pond. The water is cool but not cold. Lisa meets you, her beautiful pert breasts just above the water's surface. The two of you kiss then she breaks away and playfully makes you swim after her. You catch up with her, kiss her, and then dunk her in the water.
As your aquatic foreplay continues, the sun has slipped below the horizon and a full moon has crept over the opposite horizon.
The moon is bright and the two of you pay little attention to the fading light. You catch up with Lisa again near the shore. You share another kiss, the deepest yet. You gently take her down onto her back in the shallow water and at last slide into her. She moans with delight.
But as you make love in the shallows you begin to feel strange. Unbeknowst to you, but swimming in this particular pond under a full moon begins to cause you and Lisa to change into...