Much to your surprise you see to girls by the water's edge. Frolicking is the only word for what they seem to be doing.
They haven't seen you yet, they're just sitting by the water, stroking each other's hair, speaking in whispers, smiling and giggling at each other.
Something about the situation speaks to the voyueristic streak in you and you feel yourself getting more aroused, as the girls caress each other.
You reach down and stroke yourself through you jeans. [Stroke yourself through your clothes for a minute]
The girls remain oblivious to your presence, indeed they seem to be getting quite heated, one kissing the other's neck while caressing a boob. You unzip your fly and whip out your cock, slowly stroking yourself and the girls get more intimate. [Give you cock fifty slow strokes]