In the ocean there is a place called dragons gate (Ryū-Mon) where, without intermission large, enormous waves are ascending. Without fail, fish which cross this place become dragons. That is why this place is called dragons gate.
The big waves are no different to waves at every other place and the water is just ordinary water. Nevertheless in a mysterious way fish which cross this place will become dragons. Their skin and their body do not change - anyway, they suddenly become dragons.