Fallen: Depths of the Glarr

From the publisher's webpage:

Beyond the Namoren swamp, an old dungeon lies hidden beneath the waters. Between crumbling statues of dragons and forgotten heroes, water cascades down the ancient hallways of the labyrinth. However this dungeon is not forgotten, nor is it still. Fierce reptilian creatures now call this dark place their home. They prey on merchant barges that pass through their waters. They attack any traveler foolish enough to enter their swamp. They show they mercy. They are...the glarr. What riches do they have scurried away to the bottom of their lair? What dark power now drives them? Can you brave the Depths of the Glarr?