Exodus 7:19-20

19And the LORD said unto Moses, Say unto Aaron, Take thy rod, and stretch out thine hand over the waters of Egypt, over their rivers, over their streams, and over their pools, and over all their ponds of water, that they may become blood; and there shall be blood throughout all the land of Egypt, both in vessels of wood and in vessels of stone.

20And Moses and Aaron did so, as the LORD commanded; and he lifted up the rod, and smote the waters that were in the river, in the sight of Pharaoh, and in the sight of his servants; and all the waters that were in the river were turned to blood.