Dragons have been worshiped as the god of water in Japan since ancient times.
It is said that only carp that swim up a waterfall can transform into a dragon as the god of water.

I drew Zennyo Ryuo, the daughter of the Dragon King.
There is an anecdote that in 824, during a drought, Kukai, a Buddhist dignitary, summoned Zennyo Ryuo, the 8-year-old daughter of the Dragon King who lived in a pond in Tenjiku, and brought heavy rain to all of Japan.