I have chosen three quotations from the story which I think most vividly convey a sense of the setting.

I remembered . . . the early mornings, when the lake was cool and motionless, remembered how the bedroom smelled of the lumber it was made of and of the wet woods whose scent entered through the screen.

In this first quotation, the author draws upon the sense of smell to evoke his memories of the lake. The sense of smell is perhaps, among all the senses, the one that most effectively conjures up memories. In the quotation, the bedroom in the camp, by the lake, is described as smelling of "lumber" and of the "wet woods" outside. For anyone who has ever been in a woods when the ground is covered with wet leaves, this is quite a strong, distinctive smell, and will likely conjure up memories which will allow the readers to easily imagine themselves in the place of the narrator.

when the older boys played their mandolins and the girls sang and we ate doughnuts dipped in sugar, and how sweet the music was on the water in the shining night . . .

This second quotation draws upon three of the senses, the sense of hearing, the sense of taste, and the sense of sight. The sounds evoked are the music played by the "mandolins" and the girls singing. These sounds suggest a soft, peaceful mood. The taste is the familiar taste of "doughnuts dipped in sugar." And the sight implied by the phrase, "the water in the shining night," is perhaps of a moonlit lake, with the reflection of the silver moon shimmering on the surface of the dark water. All three senses together produce a rich, vivid setting.

Then the kettle drum, then the snare, then the bass drum and cymbals, then crackling light against the dark, and the gods grinning and licking their chops in the hills.

This third quotation describes the sound of a storm, using the metaphor of a drum kit. Each part of the kit is attributed to a different sound of the storm, conjuring up aural imagery of thunder crashing, clanging, and crackling. In this third quotation, the lightning is also described as "crackling light against the dark," and the author alludes to "the gods grinning and licking their chops." This allusion to the gods suggests that they are relishing the sounds and sights of the storm, it and also attributes to the scene an otherworldly, perhaps religious significance.

There are several instances in which E.B. White describes the stillness of the lake using sensory details and metaphors. For example, at the beginning of the story, he writes, "I remembered being very careful never to rub my paddle against the gunwale for fear of disturbing the stillness of the cathedral." He compares the lake to a cathedral, as the water has a kind of spiritual stillness and calm to it. He later writes:

When we got back for a swim before lunch, the lake was exactly where we had left it, the same number of inches from the dock, and there was only the merest suggestion of a breeze.

In this example, he uses sensory details, such as the soft breeze, to convey how still and tranquil the lake appears. The author also uses repeated instances of the way the area around the lake smells, including the "pine-laden air." He writes about "how the bedroom smelled of the lumber it was made of and of the wet woods whose scent entered through the screen." These sensory details, appealing to the sense of smell, help the reader feel like he or she is at the lake, breathing in the piney, wet woods. They strongly convey the sense of setting.

As you reread the essay, I think you want to pay attention to a couple of things.  Look at White's description of the lake from his point of view as a child to how he describes it now.  Examine how he talks of the simplicity of the lake then in comparison to the speed boats and people now.  There is language of simplicity as a child that is not present in the modern setting.  I would pay attention to the language and details that reflect this.  Another set of language and details I would pay attention to is the idea of change over time.  There is a wistful sense to the essay that talks about how White has changed.  When he was visiting the lake as a child, he was a child and remembers this conception.  This is where his pain exists now.  Time is beginning to take its toll on White, and he is finding it hard to recreate those memories, indicating time's passage.  I would pay attention to these images and details.  This is shown in the fishing rod moment, when he sees someone else embodying what he used to be.  The language or details that address the themes of change and time help convey the essence of the setting of the lake.