Revelation 8:8

And the second angel sounded, and I saw as it were a great mountain on fire cast into the sea, and a third part of the sea became blood.

Revelation 11:6

These have power to shut the heavens, so that no rain may fall in the days of their prophecy: and they have power over the waters to turn them into blood, and to smite the earth with every plague as often as they will.

Revelation 16:3-6

And the second angel poured out his vial upon the sea; and it became blood like that of a dead man: and every living soul in the sea died.

Treasury of Scripture Knowledge

Summary

Thus saith the LORD, In this thou shalt know that I am the LORD: behold, I will smite with the rod that is in mine hand upon the waters which are in the river, and they shall be turned to blood.

Bible References

And they

Revelation 8:8
And the second angel sounded, and I saw as it were a great mountain on fire cast into the sea, and a third part of the sea became blood.
Revelation 16:3
And the second angel poured out his vial upon the sea; and it became blood like that of a dead man: and every living soul in the sea died.