Ultimate shoulder rides

>I hope to upgrade my membership. This is a story from the past.
>One sunny day I went  to a lakeshore to prepare for my next university test. Lots of people were having fun on the beach and in the water. Among them I noticed two girls of about 18-19. One of them with short brown hair was wearing blue bikini and another girl was blonde in a yellow swim suit. They were playing different water games like jumping, diving under each other's legs etc.  It was almost in front of me so I could look at them over my textbook. At some stage the dark-haired girl stepped behind the blond one and put her hands on the blondie’s shoulders. I could not hear their conversation but I realized that something exciting should happen. In a few seconds the blue bikini girl started to press down the blonde’s shoulders until her friend’s head disappeared under the water. Few moments later the brunette’s body started to move up slowly and finally her nice lower part had appeared from the water with the blonde’s wet head between her tanned legs. The blue bikini girl  adjusted her weight on the blonde’s shoulders and put her hands on the blonde’s head.  The brunette continued to sit on her friend’s shoulders for a few minutes looking down at blonde’s head. Then the blonde’s turn came. She was rather attractive in her yellow bikini but she was not a good sitter. The girls lifted each other several times and returned to the beach. After a break they went into the water for another set of shoulder rides. This time the brunette tended to be on top more often because she was more confident rider. And after a second break the brunette refused to make her hair wet so the pretty blonde had to give her friend several long rides. The last shoulder ride lasted about 5-7 minutes. The blonde’s body was covered by the water except her head which from time to time disappeared like a fishing float. The brunette in  blue bikini was rocking smoothly on her friend’s shoulders and her nice ass was gliding on lake’s surface. Both girls seemed to enjoy this game.  Then the girls left and I have never seen them again.