Revelation 16:3

blood as of a dead man
Αἷμα ὡς νεκροῦ [Haima hōs nekrou] , blood as (a) dead (one). In the judgment of the second trumpet, a third of the sea became blood and a third of the living creatures in the sea died. See commentary on Revelation 8:8. Now, the remainder of the sea becomes blood, but not just blood, lifeless blood. Scripture indicates that the “life of the flesh is in the blood” (Lev. Lev. 17:11). Blood “banks” and “bloodmobiles” in our own day attest to this truth recorded by Scripture long before the medical discoveries of our time. The blood is the essential system by which nutrients arrive and waste is removed.

every living creature in the sea died
Now, the essential life-supporting mechanisms within the sea, the basis of the food chain, are destroyed. As in Egypt, the animal life within the water dies (Ex. Ex. 7:18, Ex. 7:21; Ps. Ps. 105:29). See The Plagues of Egypt and the Tribulation. Rev. 8:7+.”¹

Notes

¹ Monty S. Mills, Revelations: An Exegetical Study of the Revelation to John (Dallas, TX: 3E Ministries, 1987), Rev. 16:3.