The incident happened Monday morning at the Ventura Harbor.
The fire battalion chief says someone was trying to launch a jet ski when the Cybertruck sank.
The vehicle was completely submerged in the water when crews arrived.
They had to send down a diver to hook it up to a tow truck.
Water can be seen pouring out of the flooded truck after crews got it out of the harbor.
Authorities said no one was hurt.