Adam Clarke Bible Commentary
That saith to the deep, Be dry "Who saith to the deep, Be thou wasted" - Cyrus took Babylon by laying the bed of the Euphrates dry, and leading his army into the city by night through the empty channel of the river. This remarkable circumstance, in which the event so exactly corresponded with the prophecy, was also noted by Jeremiah, Jer 50:38; Jer 51:36.
"A drought shall be upon her waters,
and they shall be dried up: -
I will lay her sea dry
And I will scorch up her springs."
It is proper here to give some account of the means and method lay which the stratagem of Cyrus was effected.
The Euphrates in the middle of the summer, from the melting of the snows on the mountains of Armenia, like the Nile, overflows the country. In order to diminish the inundation, and to carry off the waters, two canals were made by Nebuchadnezzar a hundred miles above the city; the first on the eastern side called Naharmalca, or the Royal River, by which the Euphrates was let into the Tigris; the other on the western side, called Pallacopas, or Naharaga, (נהר אגם nahar agam, The river of the pool), by which the redundant waters were carried into a vast lake, forty miles square, contrived, not only to lessen the inundation, but for a reservoir, with sluices, to water the barren country on the Arabian side. Cyrus, by turning the whole river into the lake by the Pallacopas, laid the channel, where it ran through the city, almost dry; so that his army entered it, both above and below, by the bed of the river, the water not reaching above the middle of the thigh. By the great quantity-of water let into the lake, the sluices and dams were destroyed; and being never repaired afterwards, the waters spread over the whole country below, and reduced it to a morass, in which the river is lost. Ingens modo et navigabilis, inde tenuis rivus, despectus emoritur; et nusquam manifesto exitit effluit, ut alii omnes, sed deficit. "And thus a navigable river has been totally lost, it having no exit from this morass. No wonder then that the geographical face of this country is completely changed;" Mela Jer 3:8; Herod. 1:186, 190; Xenophon, Cyrop. vii.; Arrian vii.
Jamieson-Fausset-Brown Bible Commentary
Referring to the Euphrates, which was turned into a different channel, close to Babylon, by Cyrus, who thereby took the city. "The deep" is applied to Euphrates as "sea" (Jer 51:32, Jer 51:36). "Rivers" refers to the artificial canals from the Euphrates made to irrigate the country; when it was turned off into a different bed (namely, a lake, forty miles square, which was originally formed to receive the superfluous water in an inundation), the canals became dry.
John Gill Bible Commentary
That saith to the deep, be dry,.... The Targum is,
"that saith to Babylon, be desolate;''
and most interpreters, Jewish and Christian, understand it of Babylon, which was situated in a watery place, by rivers of water, particularly the river Euphrates, and in a low valley:
and I will dry up thy rivers; some think the allusion is to the stratagem of Cyrus, made use of, under a divine direction, to drain the river Euphrates, and make it passable for his army; by which means he surprised the city of Babylon, and took it: though others think it refers to the drying up of the Red sea and the river Jordan, which are proofs of what God can do, and a periphrasis of his power.
Tyndale Open Study Notes
44:27 The sudden depletion of natural resources at times indicates a divine judgment (see 42:15; cp. 43:20). Here, however, God’s ability to dry up streams with just a word illustrates his power to do what he said he would do through Cyrus of Persia.