What metaphors are used in On Golden Pond by Ernest Thompson?

One visual symbol in the film can be found in the movie's opening sequence, which shows in long shot (a shot taken from a considerable distance) the sun setting over Golden Pond, and the water shimmering in the golden light. This is a perfect metaphor for the relationship between Norman and Ethel Thayer, which has stood firm for a long day of forty-eight years and is now, because of Norman's age and ill health, probably approaching its end.