The Gotham City Channel is the body of water surrounding Gotham City. It is described as always being cold and icy.
Arkham Origins Incident
Both North and South Gotham are bordered by the Channel in Batman: Arkham Origins. It separates the islands from the rest of the mainland. The Penguin's ship, the Final Offer, is anchored in the Channel and experiences flooding, putting it at risk to sink. Some parts of the Channel may have been made toxic due to Joker dumping acid and various chemicals into it from the Gotham Royal Hotel.
Arkham Asylum Incident
The Gotham City Channel appears in Batman: Arkham Asylum as the borders of Arkham Island. During the events of the game, Bane, Killer Croc, and Scarecrow all end up stranded and floating in the channel, clinging onto cases of TITAN.
Arkham City Incident
The Channel reappears in Batman: Arkham City, as one of the borders of the open-air prison. The Channel separates Arkham City from mainland Gotham. At some point before the game, the Channel floods parts of Amusement Mile, completely engulfing some buildings and streets.