It appears to be lime colored water.
It replaces the default Simple Sea with a more green look.
- Despite having "river" in its name, the events of Siege could take place on a land near a sea, judging from the name of the other moat, such as the Simple Sea and the Frozen Sea.
- Even though the item itself has been removed from crafting Clan Forts, it can still be sometimes seen in Escort.
- Despite its looks and name, it does not give a poison effect.