Moses smote the waters in the river, while the Pharaoh watched. And the river turned to blood. 21 All the fish in the river died, the river stank, no one could drink from it, and there was blood everywhere in Egypt.
22 But Pharaoh's magicians knew this trick too. They smote the river with their rods and turned it into blood.
A few more words about this episode
The genealogy of Moses and Aaron (6:14-25)
I have left out a section in chapter 6 about Moses's genealogy.
Although it doesn't make for very exciting reading, it says a few things that are interesting. Here, for example is verse 6:20:
Amram took him Jochebed his father's sister to wife; and she bare him Aaron and Moses.
So Moses and Aaron (and presumably Miriam) were the products of an incestuous marriage that is condemned in 20:19.
And in verses 16-20 only four generations listed from Jacob to Moses (Jacob, Levi, Kohath, Amram, Moses).
Since Ex 12:40 says that the Israelites were enslaved for 430 years, it seems rather unlikely for there to have been only four generations in that time period.