Which are blackish by reason of the ice, and wherein the snow is hid:

Wesley's Notes

6:16 Which - Which in winter when the traveller neither needs nor desires it, are full of water congealed by the frost. Snow - Under which the water from snow, which formerly fell, and afterward was dissolved, lies hid. So he speaks not of those brooks which are fed by a constant spring, but of them which are filled by accidental falls of water or snow.

Jamieson-Fausset-Brown Bible Commentary

16. blackish-literally, "Go as a mourner in black clothing" (Ps 34:14). A vivid and poetic image to picture the stream turbid and black with melted ice and snow, descending from the mountains into the valley. In the [second] clause, the snow dissolved is, in the poet's view, "hid" in the flood [Umbreit].

Matthew Henry's Concise Commentary

6:14-30 In his prosperity Job formed great expectations from his friends, but now was disappointed. This he compares to the failing of brooks in summer. Those who rest their expectations on the creature, will find it fail when it should help them; whereas those who make God their confidence, have help in the time of need, Heb 4:16. Those who make gold their hope, sooner or later will be ashamed of it, and of their confidence in it. It is our wisdom to cease from man. Let us put all our confidence in the Rock of ages, not in broken reeds; in the Fountain of life, not in broken cisterns. The application is very close; for now ye are nothing. It were well for us, if we had always such convictions of the vanity of the creature, as we have had, or shall have, on a sick-bed, a death-bed, or in trouble of conscience. Job upbraids his friends with their hard usage. Though in want, he desired no more from them than a good look and a good word. It often happens that, even when we expect little from man, we have less; but from God, even when we expect much, we have more. Though Job differed from them, yet he was ready to yield as soon as it was made to appear that he was in error. Though Job had been in fault, yet they ought not to have given him such hard usage. His righteousness he holds fast, and will not let it go. He felt that there had not been such iniquity in him as they supposed. But it is best to commit our characters to Him who keeps our souls; in the great day every upright believer shall have praise of God.