In one of the most bizarre terrorism detection methods that has been reported over the last few years, San Francisco and other major cities have revealed their new secret weapon in the war against terror and poison in their drinking water: fish. The major cities are dropping common Bluegills (also known as Sunfish or Bream) into their drinking water tanks. The tanks have sensors monitoring the water and the fish around the clock and if the Bluegills start to show signs that there is a foreign chemical in the water, an email alert is sent out instantly.

Fish used to detect terror attacks (Yahoo)