In that day: i.e. the period of judgment foretold in Isa_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).