Backwash

Summary
Backwash is a multiplayer level in Halo 2, similiar to the campaign level on Halo: Combat Evolved called 343 Guilty Spark. It is a large swamp set on Delta Halo. You can tell it is Delta Halo, not Alpha Halo, as 2401 Penitent Tangent can be seen floating around and humming to himself. It is actually stated by the developers of Halo 2 that Backwash was originally set on Alpha Halo and based directly on the Halo: Combat Evolved campaign level, 343 Guilty Spark(Level). It is also stated that they originally had 343 Guilty Spark floating around but decided to change him to 2401 Panitent Tangent because 343 Guilty Spark's blue glow could too easily be mistaken for a Plazma Grenade flying through the air.

External Reference
Backwash