Exodus 7:19-20

The LORD said to Moses, “Tell Aaron: ‘Take the walking stick in your hand and stretch your hand over the rivers, canals, ponds, and pools in Egypt.’ The water will become blood everywhere in Egypt, both in wooden buckets and in stone jars.” So Moses and Aaron did just as the LORD had commanded. In front of the king and his officers, Aaron raised his walking stick and struck the water in the Nile River. So all the water in the Nile changed into blood.