Trivia: At some of the theaters showing this film, when the shark explodes, the "guts" are actually E.T. dolls that were being sold.
Trivia: As originally envisioned, this film was going to be a parody titled "Jaws 3, People 0," as it was felt that a third film wouldn't necessarily work. The producers of the first two films brought in writers from National Lampoon to write the script and it almost went into production, but the studio shut them down at the last minute. "Jaws" producer David Brown maintained till his death that "Jaws 3, People 0" would have been much more interesting and entertaining than "Jaws 3-D" turned out to be.
Answer: The lagoon was part of the theme park. Artificial with specific mammals inhabitants inside, warm and friendly.