The shark's infamous roar during the climax actually comes from a Tom and Jerry cartoon called The Milky Waif (1946). Reportedly, this was actually done because the sound editor refused to make an original sound effect, thinking that the idea of a shark roaring was ridiculous.
This is one of Michael Caine's notorious "paycheck movies", along with The Swarm (1978), Ashanti (1979), Beyond the Poseidon Adventure (1979), The Island (1980), The Hand (1981), Blame It on Rio (1984) and On Deadly Ground (1994). When Caine was asked about this movie in an interview, he answered, "I have never seen it, but by all accounts it is terrible. However, I have seen the house that it built, and it is terrific."
The water in the tank where the climax was shot was filled with blue dye, which turned Michael Caine's and Lorraine Gary's hair blue.
Michael Caine said, "Won an Oscar, built a house, and had a great holiday. Not bad for a flop movie." He was paid $1.5 million for seven days work in the Bahamas, and the schedule was so tight that the producers were unable to spare him so he could attend the Academy Awards, and he went on to win the Best Actor in a Supporting Role Oscar for Hannah and Her Sisters (1986).
Lorraine Gary briefly came out of retirement (following 1941 (1979)) to reprise the role of Ellen Brody. This film stands as her final acting role to date.