Adam Clarke on Job 40:23

Behold, he drinketh up a river - A similar mode of expression, and of precisely the same meaning, as that in Job 39:24 : "He swalloweth the ground with fierceness." No river can stop his course: he wades through all; stems every tide and torrent; and hurries not as though he were in danger.

He trusteth that he can draw up Jordan - Even when the river overflows its banks, it is no stoppage to him: though the whole impetuosity of its stream rush against his mouth, he is not afraid. Mr. Good has seized the true idea in his translation of this verse: - "If the stream rage, he revileth not:

He is unmoved, though Jordan rush against his mouth."

From this mention of Jordan it is probable that the behemoth was once an inhabitant of the mountains, marshes, and woods, of the land of Palestine.