Revelation 16:3
Then the second [angel] poured out his bowl into the ocean, making it turn into blood like that of a dead person, and every living thing in the ocean died.
Revelation 8:8-9
[When] the second angel sounded its trumpet [I saw] what seemed like a huge mountain, ablaze with fire, being thrown into the ocean. And one third of the ocean turned to blood,
Revelation 11:6
These witnesses have the authority to shut the sky up so that it does not rain during the time they are prophesying. And they have the authority to turn the waters into blood, and to strike the earth with every kind of plague whenever they want to.
Revelation 10:2
He held in his hand a little book [i.e., scroll] which was open. And he placed his right foot on the ocean and his left foot on the land,
Revelation 13:1
And I saw a beast coming up out of the ocean. It had ten horns and seven heads, and [it had] ten crowns on his horns and on each head there was a blasphemous name [i.e., a name that slandered God].