Making use of a short-lived revival of the 3-D format, Jaws 3D saw a huge great white shark accidentally swimming into SeaWorld Florida and eating its way through the staff when it becomes trapped. Despite such a unique locale, the sequel is weirdly lifeless for long stretches and is more concerned with the dull relationship between Mike Brody (Dennis Quaid) and his girlfriend Kathryn (Bess Armstrong) than the shark. The film is also infamous for its terrible special effects, including the finale "showstopper" where Jaws 3's shark smashes through an underwater control room.
In a time before franchises became a big thing, Jaws 3 still performed respectably at the box office. While the previous movies played fast and loose with the behavior and sizes of real great white sharks, the third film dialed the implausibility way higher. In addition to growling constantly - impossible, since sharks have no vocal cords - or swimming backward, Jaws 3's shark is also 35 feet in length. A theory suggests that instead of being a great white, Jaws 3's beast is actually a megalodon.
The largest great white sharks on record have measured between 21 to 23 feet in length at the maximum, so obviously, Jaws 3's shark surpasses that. This suggests it's not a great white at all and could be a megalodon. A common misconception is that the megalodon and the great white shark are closely related, which is something scientists have since debunked. That's not to say they looked entirely dissimilar, and according to Smithsonian Ocean, male megs ranged in length from 34 to 47 feet while females averaged 44 to 56 feet. That makes this Jaws 3 theory somewhat plausible - although how the beast isn't extinct is another question.
That said, Jaws 3's story contradicts this reading. A key storyline sees the staff capture a baby great white, who later dies in captivity. Kathryn - a marine biologist - later identifies the creature as the baby shark's mother, obviously identifying the shark as a great white too. While Kathryn might be mistaken, the odds of two unrelated sharks - a great white and a megalodon - happening to swim into SeaWorld at the same time is borderline astronomical. It's also likely the only consideration Jaws 3's - which Speilberg rejected - filmmakers gave to the shark's impossible size is the notion that bigger was scarier.