Rashi on Exodus 7:19/רש"י על שמות ז׳:י״ט

1אמר אל אהרן SAY UNTO AARON — Because the river had protected Moses when he was cast into it, therefore it was not smitten by him neither at the plague of blood nor at that of frogs, but it was smitten by Aaron (Exodus Rabbah 9:10).

2נהרתם THEIR STREAMS — These are the flowing rivers, just like our rivers in France.

3יאריהם — These are canals which convey water being made by human agency and extending from the river bank into the fields. The waters of the Nile increase in volume and rise by way of these canals and so irrigate the fields.

4אגמיהם — A collection of waters that neither spring up from beneath the ground nor flow along, but which remain in one spot. In old French they call it étang.

5בכל ארץ מצרים [THERE WILL BE BLOOD] THROUGHOUT ALL THE LAND OF EGYPT— also in their bathing establishments and in the baths in their houses.

6ובעצים ובאבנים — the water which happened to be BOTH IN vessels of WOOD AND in vessels of STONE.