According to the prologue of Where the Crawdads Sing, the difference between a marsh and a swamp is that the former is "a space of light, where grass grows in water, and water flows into the sky."

Swamp water, on the other hand, is "still and dark, having swallowed the light in its muddy throat." Unlike the marsh, the swamp is also a place of death and decomposition, where life "decays and reeks."

The distinction between a marsh and a swamp is significant throughout the story in that the marsh is an important component of Kya's identity; it's part of who she is. The marsh, with its brightness and space, is something that will never leave her, and she, for her part, will never leave the land.

Unlike the swamp, which is, as we have already seen, a place of death and decay, the marsh is positively bursting at the seams with life. It is primarily because of its life-giving and life-sustaining nature that Kya feels a sense of comfort there that she can feel nowhere else. She belongs in the marsh; it has entered into her soul, into her very being, and in doing so has forged an indissoluble connection between Kya and the land in which she has grown up.