A mountain lake is still water reached only by climbing, so dream books read it as clarity and peace earned through effort. Its cold purity is linked to a fresh, uncluttered mind.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.