Revelation 8:8

And the second angel sounded; and it was as if a great mountain, burning with fire, was cast into the sea;

Revelation 11:6

These have power to shut heaven, so that no rain shall be showered down in the days of their prophecy; they have power over the waters, to turn them to blood, and to smite the earth as often as they will, with every plague.

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 that was 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 it was as if a great mountain, burning with fire, was cast into the sea;
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 that was in the sea died.