Albert Barnes Commentary Psalms 77:16

"The waters saw thee, O God; The waters saw thee, they were afraid: The depths also trembled." — Psalms 77:16 (ASV)

The waters saw thee ... - The waters of the Red Sea and the Jordan. There is great sublimity in this expression, in representing the waters as conscious of the presence of God and as fleeing in consternation at His presence. Compare (Revelation 20:11; Habakkuk 3:10–11).

They were afraid - On the word used here—חול chûl—see (Psalms 10:5, note; Psalms 55:4, note). It may mean here to tremble or quake, as in pain (Deuteronomy 2:25; Joel 2:6). Alarm, distress, anguish, came over the waters at the presence of God; and they trembled, and fled.

The depths also were troubled - The deep waters, or the waters in the depths. It was not a ripple on the surface, but the very depths—the usually calm and undisturbed waters that lie below the surface—were heaved into commotion at the divine presence.