As you swim playfully in the water, you gradually become more and more graceful as you swim in the water. You swim faster than you ever remember swimming before, almost as if you were meant to be here, to swim in the waters of this wonderful stream. Pretty soon you're like a bullet in the water, almost leaping from the surface as you head there. When you surface for a breath, you throw back your head and laugh, your long hair flying back behind you. You never noticed how long your hair was-- you could have sworn that you had gotten a haircut just a week or two ago-- but at this point it doesn't matter, you feel so good swimming around and playing in the stream.
In addition, your laugh has grown higher and more musical, but you chalk it up to just how much fun you're having there in the water. You dive back in with a loud splash. Several times you do this, each time spending just a little longer underwater before you surface. The water is making you feel wonderfully, your skin clearing up, and your body slimming down. You don't even notice the added weight on your chest until it is far too late, but it doesn't even matter to you. Your fins feel wonderful in the warm water.... FINS?
You are suddenly jerked back to reality and you tread water, looking down at yourself. You have entirely transformed, to the point that you are nearly unrecognizable. Your body is abundantly feminine now, with a pair of D cup breasts on your chest, a slim, hourglass figure, and it ends in a glistening silvery blue tail. Your hair, once short and brown, is now wavy, long, and hangs down past your shoulders. You feel your face. Very rounded, with full lips. You've turned into a woman. No, a mermaid.
You are about to start panicking, when you hear the sound of splashing nearby...