And they shall turn the rivers far away - (האזיּחוּ he'ezenı̂ychû), probably from זנח zânach, “to have an offensive smell; to be rancid, or putrid.” The word in this form occurs nowhere else. It is in the Hiphil conjugation, and is probably a form made from a mixture with the Chaldee. The sense is not doubtful. It means ‘the rivers shall become putrid - or have an offensive smell;’ that is, shall become stagnant, and send forth unwholesome “miasmata” producing sickness, as stagnant waters often do. The Vulgate renders it, ‘And the rivers shall fail.’ The Septuagint, ‘And the Egyptians shall drink the waters from the sea, but the river shall fail, and be dried up, and the rivers shall fail, and the streams (διὼρυχες diōruches) of the river, and all the assembling (συναγωγή sunagōgē) waters shall be dried up.’
And the brooks of defense - Hebrew, ‘The rivers of מצור mâtsôr. The word מצור mâtsôr often means “straitness, affliction;” then a siege, a wall, a bulwark, a fortification. But, probably, it here means “Egypt,” or the same as מצרים mı̂tserayı̂m (compare Isaiah 37:25; 2 Kings 18:24; Mark 7:12). Perhaps the Hebrews may have thought of Egypt as a strongly fortified place, and thus have given the name to it; or possibly this may have been a modification of the name “Mitsraim.”
The reeds and flags - Which grew on the banks of the Nile - the papyrus, etc. (see the note at Isaiah 18:2)