Water Hazard is the last of the five chapters from the original Half-Life 2 that were modded for functionality within Left 4 Dead 2, making a significant portion of the original story playable in this new setting. Water Hazard takes the player on a speedy hover boat-based journey through swampland and urban marshes. Though the original level was a quick one in Half-Life 2, Water Hazard is the hardest of the five chapters available in Left 4 Dead 2.