In that day: i.e. the period of judgment foretold in Isaiah 26:21.
leviathan. Three great aquatic animals are here mentioned: probably referring to Israel's three great enemies: Assyria (with Nineveh, on the Tigris); Babylon (on the Euphrates); and Egypt (on the Nile); with Satan himself behind them all, as their great instigator.
piercing. fleeing, or fugitive (like the Tigris). crooked tortuous (like the winding Euphrates).
dragon. the crocodile of the Nile.
sea. the Nile, as in Isaiah 19:5.Nahum 3:8.