The eponymous Essex Serpent is the most symbolic presence in the book, even if it does not technically exist. There are three distinct versions of the Essex Serpent: the dead fish that washes up on the shore, the boat that belonged to Banks and was lost on the estuary, and the mythological creature that only existed in the minds of the villagers. There are distinct symbolic means attached to all three.

The first Serpent discovered by the people of Aldwinter helps to dismiss the notion that the creature was real. When a dead fish (likely to be a large oarfish) washes up on the shore of the estuary, a terrible smell permeates the village. When the villagers investigate, they find that their serpentine threat is little more than a harmless fish. When its gut is kicked, it splits open and reveals a tangle of tapeworms, who have been starving the creature from the inside out. The dead fish is a metaphor for the villagers’ belief. Like their beliefs, the fish has been starved of nutrition. As they have turned away from Will’s teachings and come to doubt him, they have moved further away from logic and reason.