Yes
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Of course he can, he just chooses not to.
The big three of the Olympians were Zeus, Poseidon, and Hades. When ever two of these three came into conflict with each other they chose arbitration rather than battle - this demonstrates self-control.
eg. When Hades raped Zeus' daughter Persephone (kidnapped her and forced her to marry him) Zeus initially did nothing, preferring not to contend with Hades. It was only after extensive protests by Ceres (the girl's mother) that Zeus worked out a compromise that was decidedly in Hades' favour.
eg. When Zeus and Poseidon contended over the nymph Thetis, Prometheus arbitrated and gave the nymph to a mortal king so neither of the Gods could have her.
Poseidon's area of power and control is the sea. Any water source can be controlled by him too.
Poseidon is the Greek God of oceans, horses and earthquakes. he has control over anything to do with the sea
Poseidon controls the sea because he is the god of the sea.
Poseidon fought with other gods: Zeus himself, Hera, Dionysus, Helius
Seeing as Poseidon turned himself into a horse to mate with Demeter, the answer is yes.
Poseidon was known for the god of the sea. He can control any water thing.
Poseidon inspired greeks by having control of water. Which is the answer to thirst.
Zeus got the earth, Poseidon the sea, and Hades the underworld.
In Greek Mythology there were three main gods. Zeus had control over the skies, Poseidon had control had control over the seas, and Hades had control over hell.
He is a god; presumably he believed in himself.
The cast of The Poseidon Project - 2013 includes: George Malcolmson as himself Doreen Ridsdale as herself Steven Schwankert as himself
Poseidon's Trident did give powers, for example he can control the waves and size, time and width of them!