The scene at the beginning of chapter six is the same as the one at the beginning of the novel. The time of day is late afternoon, a pleasant shady feel is present, and the water is a calming deep green. This initial description gives the reader the sense of tranquility.
Suddenly, the heron attacks a water snake and they struggle, and at the same time a strong wind ripples the water into waves and whips through the trees disrupting the tranquil moment.
This is symbolic in that at that time, Lennie approaches, symbolizes the trouble that is about to accompany him.