Nymphs are "minor" goddesses. But "minor" doesn't mean weak. It means local.
A great god rules a wide principle. A nymph belongs to one fountain, one grove, and carries its character in her bones. The air around her smells like whatever land holds her. Wet leaves, salt, pine resin, sun-warmed bark.
She's divine, but she can die. If the spring dries up, so does she. That quiet fragility is the part most retellings skip.