What does Exodus 7:21 mean?

The water in the river turned into blood, and every living thing in it died. The river started to stink so badly that the Egyptians couldn’t drink from it. Blood was everywhere in Egypt. Exodus 7:21 - Modern Text Bible

(This verse describes the first plague’s devastating effect: the Nile, Egypt’s lifeline, becomes undrinkable and deadly, showing God’s power over what the Egyptians trusted most.)