Gatsby's first swim of the summer is ironically also his last swim. After spending the night checking on Daisy, he retreats to his pool for a cool and relaxing swim. This is where Wilson (having been sent by Tom) finds the unaware Gatsby and shots him.
At two o’clock Gatsby put on his bathing-suit and left word with the butler that if any one phoned word was to be brought to him at the pool. He stopped at the garage for a pneumatic mattress that had amused his guests during the summer, and the chauffeur helped him pump it up. Then he gave instructions that the open car wasn’t to be taken out under any circumstances — and this was strange, because the front right fender needed repair.
He got the idea when the gardener, the only remaining servant, suggests that he drain the pool. Since it hadn't been used all summer, Gatsby tells him to wait. At 2, Gatsby leaves word that if anyone should call (he's still hoping Daisy will call) he will be in the pool.