The idea of change is one of the most important elements in White's essay.
The passage of time in White's identity is one aspect of change that takes place on the lake. White used to go to the lake as a child and now goes as a father. His perspective about the lake and what it means has become amplified because of time's passage:
I seemed to be living a dual existence. I would be in the middle of some simple act, I would be picking up a bait box or laying down a table fork, or I would be saying something, and suddenly it would be not I but my father who was saying the words or making the gesture. It gave me a creepy sensation.
There is a depth to White's experience because he sees it as both a child and a man. This is a change to what he had previously experienced when he was younger.
Superficial changes are White's only real physical reminder that time has passed. For example, "the sound of the outboard motors" represents how things have changed from then to now. The inboard motors have been replaced with the outboard ones. As a result, the sense of sound has changed at the lake. The cosmetic appearance of the waitresses is another sensory example of change. White notes how the girls of now have screen starlets to model their looks after.
I think that the final change is White's understanding that time will invariably pass. Just as White has progressed from child to father, he recognizes at story's end that there is more change to come:
I watched him, his hard little body, skinny and bare, saw him wince slightly as he pulled up around his vitals the small, soggy, icy garment. As he buckled the swollen belt suddenly my groin felt the chill of death.
Int the end, White acknowledges that time cannot stop. The change that he experiences, "the chill of death," is one where he understands his own mortality in the midst of reveling in memory. This is a change that takes place on the lake. It is one that reminds White of his temporary existence.