The Secret Sea is a metaphysical realm composed of the shared imagination of humanity. The Lady of the Lake is the spirit caretaker of this mystic realm. Aquaman is its champion.
Some water nymphs are also residents of the Secret Sea.
Hand of the Waterbearer
Aquaman's mystic water hand is composed of this water. It enhances many of his abilities and grants him healing powers. In addition, the water could alter density, be used to scry or search, negate magic, manipulate water, traverse dimensions and separate from Aquaman and function independently.
If the hand is used in a violent manner or the death touch is used, the bearer experiences great pain and can possibly die. Overuse of the hand for violent means will summon the Thirst to attack the Secret Sea directly. This was no longer a problem as Orin was able to best the thirst who was his dark half as the waterbearer.