Ramban

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, for this one [referred to here] is in the extreme east. The verse mentions also, There is the bdellium, 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, 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.