4 The third angel poured out his bowl into the rivers and the springs of water, and they became blood.
Revelation 16:4 Cross References - Common
Revelation 8:10-11
10 The third angel sounded his trumpet, and a great star fell from heaven, blazing like a torch, and it fell on a third of the rivers and on the springs of water.
11 The name of the star is Wormwood. A third of the waters became Wormwood, and many men died from the waters, because they were made bitter.
Revelation 14:7
7 and he said with a loud voice, "Fear God, and give him glory, because the hour of his judgment has come; worship him who made the heaven and the earth and sea and springs of water."
Revelation 16:5
5 And I heard the angel of the waters say, "Righteous are you, who are and who were, O Holy One, because you judged these things;