Early human relationships with water were expressed through beliefs in serpentine aquatic deities: rainbow-colored, feathered or horned serpents, giant anacondas, and dragons. Representing the powers of water, these beings were bringers of life and sustenance, world creators, ancestors, guardian spirits, and lawmakers. Worshipped and appeased, they embodied people's respect for water and its vital role in sustaining all living things. Yet today, though we still recognize that "water is life," fresh- and saltwater ecosystems have been critically compromised by human activities. This major study of water beings and what has happened to them in different cultural and historical contexts demonstrates how and why some--but not all--societies have moved from worshipping water to wreaking havoc upon it and asks what we can do to turn the tide.