passages are stopped - The guarded fords of the Euphrates are occupied by the enemy (see on Jer 50:38).
reeds ... burned - literally, “the marsh.” After draining off the river, Cyrus “burned” the stockade of dense tree-like “reeds” on its banks, forming the outworks of the city’s fortifications. The burning of these would give the appearance of the marsh or river itself being on “fire.”