“Then the second angel poured out his bowl on the sea, and it became like the blood of a corpse. And everything in the sea died.” Revelation16:3
The second bowl is poured out on the sea, turning the water “into blood like that of a dead person, and every living thing in the sea died”. A third of the sea life had already perished with the sounding of the second trumpet, and now the rest of the sea life is gone. The oceans are dead.
One of the reasons that the bowl judgment will be so devastating is that their effects are cumulative. Before the first bowl is complete the angel will pour out the second bowl. Exactly what supernatural means God will use to destroy the oceans is not revealed, but the effects will resemble those of the phenomenon known as the red tide, concentrated, toxic species of algae kill higher forms of marine life, including shellfish, fish, and marine mammals. The stench from the dead, decaying bodies of every living thing in the sea will be unimaginable. The transforming of the world’s sea into pools of stinking death will be a graphic testimony to the wickedness of man and a reversal to the day when God originally gave life to all sea creatures. “So God created great sea creatures and every living thing that scurries and swarms in the water, and every sort of bird—each producing offspring of the same kind. And God saw that it was good.” (Genesis 1:21) The sea… became blood: Revelation 8:8-9 described a partial contamination of the sea. Here the contamination is made complete. The sea doesn’t necessarily become blood, but as of a corpse’s blood. It will match the appearance and sickening character of the blood in a dead body.