"Hydroelectric power plant in the heart of Pakistan. Fast, close quarters fights on each lane. Beware of the spillway."
— Map description
Hydro is a map multiplayer included in the Call of Duty: Black Ops II downloadable content pack Revolution. It takes place on a large hydroelectric dam facility set in Pakistan, which contains multiple chokepoints.
At around the halfway point of each round, a Pakistani announcer is heard via the speakers. After a few seconds, the spillway in the middle of the map is filled with water for a small period of time. The rushing water will kill anyone and anything (including Scorestreaks and equipment).