When Arwen escapes from the Black Riders through the river by flooding them, the spell she speaks isn't subtitled. According to the Encyclopedy of Arda, she says: "Nîn o Chithaeglir lasto beth daer; rimmo nín Bruinen dan in Ulaer", which means roughly "Waters of the Hithaeglir, hear the word of power, rush, waters of Bruinen, against the Ringwraiths"