A dam holds back a great weight of water, so tradition reads it as emotions being held in check. A strong dam stands for control; a cracking one for pressure close to breaking through.
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.