Yes and of all bodies of water.
Yes, he was the Greek God of water, The King of the seas.
Poseidon's duties are to protect all aquatic creatures, the seas, and to protect his family (An educated guess)
He ruled all the seas since he split the earth with his two brothers zues and hades zues got the sky hades got the underworld and POSEIDON RULED ALL OF THE SEAS AND OCEANS AND BODIES OF WATER.
Poseidon is the ancient god of the Seas.
The seas.
Poseidon
Poseidon, god of the seas and Hades, god of the underworld
Poseidon killed many that travel the seas
Poseidon.
God of the seas
The myth of how Athens was named. He created horses. In the story of Pyrhha and Deucalion. Theseus and the Minotaur. The story of Odysseus. Perseus and Medusa The myth of creation The war of troy. And basically many other stories involving the sea.
Poseidon is the king of oceans and seas (if you refer to Greek stuff.) The Roman equivalent is Neptune. Unless you don't believe in Greek and Roman stuff, I don't have an answer for you.