Exodus 7:23-25

Revised Standard Version

²³ Pharaoh turned and went into his house, and he did not lay even this to heart. ²⁴ And all the Egyptians dug round about the Nile for water to drink, for they could not drink the water of the Nile.

The Second Plague: Frogs

²⁵ Seven days passed after the Lord had struck the Nile.