Is there historical evidence of the third angel's pouring out of his bowl? If we look for rivers and springs turning to actual blood, the answer is, No. But when we understand (in step with the abundant symbolism in Revelation) that the point of the plague is to emphasis the prevalence of death, the answer is, Yes. In today’s world, for example, so much water from rivers and springs is undrinkable due to some form of pollution. The Lord wants us to know that his hand is behind it in accordance with the promise of Genesis 2:17.
4 The third angel poured out his bowl into the rivers and the springs of water, and they became blood.