Question

In "Through the Tunnel," the underwater tunnel that Jerry is determined to swim through may be seen as a symbol for

Answer 1

What I think it is, is that the first, safe and happy beach is most likely him living his best life with his mother, and all goes well.
The next one represents what becomes of his life. He doesn't have his mother, and he's becoming an adult.
The tunnel is perhaps what Jerry goes through to gain access to this new unpredictable future in store for him.
Hope this helps!

Answer 2

The most important characters in this story are Jerry, his mother and the group of local boys. Jerry is seen as still being under the wings of his protective mother, always craving for her love: in another way, in safe waters.

When Jerry meets these local boys, they challenge him to pass through the rock tunnel. As he goes deeper into this tunnel, he goes away from these safe water. He realises that he needs independance and autonomy from his controlling mother.

The tunnel in the story means a stage which every children need to go through to become independant from their parents.