Exodus 7:20-21

Moses and Aaron did as the LORD commanded. In the sight of Pharaoh and in the sight of his servants he lifted up the staff and struck the water in the Nile, and all the water in the Nile turned into blood. And the fish in the Nile died, and the Nile stank, so that the Egyptians could not drink water from the Nile. There was blood throughout all the land of Egypt.