John Calvin Commentary Isaiah 19:7

"The meadows by the Nile, by the brink of the Nile, and all the sown fields of the Nile, shall become dry, be driven away, and be no more." — Isaiah 19:7 (ASV)

And the reed and the rush shall wither. He mentions the reed and the rush, because they had an abundance of them and used them for various purposes; or, it could be thought to mean that the marshes will be dried up.

By the mouth of the brooks. Some render it embankments, but it rather means the fountain itself, which is seldom dried up, even if torrents or rivers fail. By the mouth, therefore, he means the source of the river that will be dried up so that no part of the country can be watered.

Though the source of the Nile was at a great distance, yet it was not without reason that the Prophet threatened that the river, on whose waters the fertility of almost the whole land depended, would be dried up at its very source. For in that country rain seldom falls, but its place is supplied each year by the Nile.

If that river overflows only scantily, it threatens scarcity and famine; and therefore, when the Prophet threatens that it will be dried up, he means that the whole country will be barren. For this reason, he also says that even at its very mouth, from which the waters spring up, there will be a lack of water, so that in that place the herbs will be withered.