Kommentar zu Bereschit 2:11

פישון PISHON — This is the Nile, the River of Egypt. Because its waters grow plentiful and rise and water the land, it is called Pishon, the name being of the same root as the verb in (Habakkuk 1:8) ופשו פרשיו “and their horsemen increased”; another interpretation of the name Pishon is: it is so called because it grows flax (פשתן) (Genesis Rabbah 16:2) for it is said with reference to Egypt (Isaiah 19:9) “Moreover they that work in combed flax, shall be ashamed.”

THE LAND OF HAVILAH, WHERE THERE IS GOLD. This is to explain that it is not the Havilah of Egypt, concerning which it is said, And they dwelt from Havilah unto Shur, that is before Egypt,³⁴⁵Genesis 25:18. for this one [referred to here] is in the extreme east. The verse mentions also, There is the bdellium,³⁴⁶Verse 12. in praise of the river, that in the sand that is in it and on its bank there is found that good gold, the bdellium and the onyx stone. For these things are found in rivers; in some, silver can be found. Similarly, the bdellium and precious stones are found mostly in rivers.
In the opinion of former scholars,³⁴⁷Rabbeinu Saadia Gaon and Rashi. Pishon is the Nile of Egypt; it compasses this entire land of Havilah, and comes from there and passes the whole land of Egypt until it falls into the great sea at Alexandria in Egypt.

שם אחד פישון, [The Torah] informed us of the praise of the river that irrigates the garden that is not known to us by informing us of the rivers that branch off from it that are known by their praised size and the goodness of their water and the goodness of their fruit.