Daryl Hannah, a vegetarian, refused to eat real lobster for the restaurant scene. The crew scooped out the insides of real, cooked lobsters and filled them with a thick, tofu-like paste. In an interview for 'Biography (1990)', Director Ron Howard said Hannah cried after each take over the deaths of the lobsters for their shells.
While Allen is offering girls names to the mermaid before she settled on Madison, the last two he suggests are Elizabeth and Samantha. Elizabeth Hanks is Tom Hanks's daughter and Samantha Lewes was his then-wife.
The "Crazy Eddie" commercial that surprises Madison was for a real electronics store. Eddie and Sam M. Antar opened Crazy Eddie in Brooklyn, NY in 1971. Their spokesman was WPIX-FM disc jockey Jerry "Dr. Jerry" Carroll, whose frenetic nonstop sales pitch was based on used car salesman Earl "Madman" Muntz. The pitch always ended with "Crazy Eddie, his prices are IN-SA-A-A-A-A-A-ANE!" The chain grew to 43 stores in 4 states. It closed in 1989 after charges of fraud and security violations.
The map from the shipwreck that Madison uses to find Allen's home is an old map of the Province of New York. It bears the name 'His Excellency William Tryon Esq.' Tyron was the colonial governor of the Province of New York from 1771 to 1780.
According to the documentary on the Splash: 20th Anniversary Edition DVD in 2004, Hannah had been swimming "mermaid" style with her legs bound together since she was a child, due to her fascination with Hans Christian Andersen's "The Little Mermaid" story.
In the documentary contained on the 20th-anniversary Splash! DVD, Tom Hanks recalled how the other cast members would drop French fries over the side of the tank to her as though she were a trained sea mammal, for she couldn't leave the water while her legs were "shrink-wrapped."