Jamieson, Fausset and Brown on 2 Kings 6:6

6. cut down a stick, and cast it in thither--Although this means was used, it had no natural adaptation to make the iron swim. Besides, the Jordan is at Jericho so deep and rapid that there were one thousand chances to one against the stick falling into the hole of the axe-head. All attempts to account for the recovery of the lost implement on such a theory must be rejected.

the iron did swim--only by the miraculous exertion of Elisha's power.

2Ki 6:8-17. Discloses the King of Syria's Counsel.