Peosiedon was the god of the sea, but he was also a god of many other things like, earthquakes. He could control earthquakes which is one of the most destructive natural disasters there are. He can also cause floods from controlling water. He can cause Droughts. He is also the god of horses.
Many gods ruled the waters beside Pontus. Nereus, and Poseidon. Posiedons son Triton trumpeted the noises of moving water. His son proteus changed shape at will. As seas seemed to do to the ancient Greeks. The titan Oceanus was a continuous water loop: the connected. System of the earths five oceans. Then there were nymphs, fresh water nymphs and three mortals who became sea divinities. The variety of gods may reflect Ancient Greek knowledge of the complexities of the water systems.