The Archetypes and The Collective Unconscious (Collected Works of C.G. Jung Vol.9 Part 1)
True, whoever looks into the mirror of the water will see first of all his own face.
Whoever goes to himself risks a confrontation with himself. . . .
The meeting with oneself is, at first, the meeting with one’s own shadow.
The shadow is a tight passage, a narrow door, whose painful constriction no one is spared who goes down to the deep well.
But one must learn to know oneself in order to know who one is.
For what comes after the door is, surprisingly enough, a boundless expanse full of unprecedented uncertainty, with apparently no inside and no outside, no above and no below, no here and no there, no mine and no thine, no good and no bad.
It is the world of water, where all life floats in suspension; where the realm of the sympathetic system, the soul of everything living, begins; where I am indivisibly this and that; where I experience the other in myself and the other-than-myself experiences me. . . .
Our concern with the unconscious has become a vital question, a question of spiritual being or non-being.
All those who have had an experience like that mentioned in the dream know that the treasure lies in the depths of the water and will try to salvage it.
As they must never forget who they are, they must on no account imperil their consciousness.
They will keep their standpoint firmly anchored to the earth, and will thus—to preserve the metaphor—become fishers who catch with hook and net what swims in the water. . .
Whoever looks into the water sees his own image, but behind it living creatures soon loom up; fishes, presumably, harmless dwellers of the deep—harmless, if only the lake were not haunted.
They are water-beings of a peculiar sort.
Sometimes a nixie gets into the fisherman’s net, a female, half-human fish.
Nixies are entrancing creatures. ~Carl Jung, Archetypes of the Collective Unconscious, CW 9, §§ 43–52.