My girlfriend Donna and I were invited to go water-skiing, and found time for a much more rewarding adventure.
Our families were ardent hunters and fishermen; they owned a very isolated camp, accessible only by boat, which we younger members soon realized was in a great location for water skiing. After we became proficient skiers, we soon understood that once out of sight no one at the camp could possibly know what we were up to.
So one fateful day, when Donna and I took our turn, we pulled the boat over to the bank, and did a little kissing and anatomical exploration standing at boat side, so that the boat was between us and anyone who happened to be passing by. These pleasantries got hotter and hotter until we were going at it completely nude with only our heads and shoulders out of the water.
At first we just masturbated one another, but as things progressed we did outercourse (penis between girl's legs just below vulva) Then I resumed fingering her clit until she had a shattering orgasm. After the first acquatic diddle, we never did it underwater again. All our subsequent diddles were either in my old van or motels.