Patchett creates a vivid portrayal of the Amazon rainforest's beauty and dangers. The jungle symbolizes the unknown that Marina must face, including exotic animals, impenetrable vegetation, and the mysterious Lakashi natives who have called the river home for centuries.

The story centers on ethical questions about scientific boundaries. Dr. Swenson studies the fertility of Lakashi women who can bear children into old age, forcing Marina to confront questions about how far one should go in pursuit of scientific knowledge.

Marina's journey is both physical and personal, requiring her to overcome fears, leave her comfort zone, and make difficult decisions. She evolves from an insecure scientist into a strong, independent woman.