This is a lake to give offerings to the Sanbi. Give a good offering = good luck, give a bad offering = well lets just say he could wash a tidal wave over Kirigakure. This is however not a very large lake, but the sanbi can travel back and forth between lakes and oceans. So really only about his head and part of his back can fit in the lake without the water being completely drained from it.
occ- im only useing this cause there is nobody with the sanbi yet, but once there is i probably wont use this anymore.