To Jerry, the wild bay represents adventure, danger, and an opportunity to exert his individuality.
In previous years, Jerry has always stayed on the sandy beach with his mother. To him, the beach possibly represents safety, comfort, and the unyielding sense of being tied to his mother's apron strings. So, as he looks across at the "wild and rocky bay," Jerry sees an opportunity to put his emerging masculine identity to the test.
Sensing that she needs to refrain from overly coddling her son, Jerry's mother gives him permission to explore the bay. Ecstatic with the possibilities that await him, Jerry swims out to sea and eventually ends up on the other side of the bay. There, he sees some boys dive off a congregation of rocks, and finally, he notices how each of the boys take turns swimming through an underwater tunnel.
Jerry sees this challenge as an invitation to prove his courage. Even though the boys see his presence as an intrusion at best, Jerry feels the need to prove to himself that he's able to do what the bigger boys have done. So begins his adventure to conquer the mysteries of the underwater tunnel, and in his eventual victory, Jerry finds the affirmation that he's looking for.