A Whale in the Bay is a covert term to advise of the unwelcomed presence of an undercover investigator amongst the ranks. The term has evolved as a means of communicating that there are others present, making it difficult to speak freely during a telephone conversation.
It was identified as a police term during an Australian royal commission into police corruption in the 1980s where corrupt officers would warn others of an internal investigation by mentioning that there was "a whale in the bay" - a normally noteable event on the Australian east coast.
by Lucky Pounder September 2, 2014