The director admitted to BBC Breakfast that he would probably use computer technology if he were making his breakthrough movie Jaws today.
Spielberg said: "Today, I would probably shoot a Jaws movie with CGI, but you know something? The audience can tell the difference.
"The second you see a million soldiers charging, you know that no-one hired a million soldiers charging any place in the world, and you know that it's artificial."
He added: "I think one of the the reasons Jaws was so effective was it was authentic.
"Just those small pieces [of footage] that were used in the cutting of the film gave the shark some bite."
Asked if he would ever return to the series, Spielberg said: "No, the only way I'm going back on the water is on a pleasure cruise! I hated being on the water, I hated shooting that movie.
"The movie really resulted in... it just really started my career, so I can't ever [deny] how important the film was to my career, but making a movie on the water is insane!"
Of the use of CGI in new movie War Horse, Spielberg said: "There are only three shots in the film that aren't real horses, and those are pretty obvious shots."
He continued of shooting in Dartmoor: "There is no place like it in the world. When I got to Dartmoor, I suddenly realised that I had a third character that I had to include in War Horse, and that was the land and the sky. so Dartmoor plays a major role.
"We had three days of amazing sunsets, and we actually took advantage of those. There is no sky replacement."
Spielberg added: "You know, audiences are so used to digital enhancements or replacements that they don't trust cinema anymore.
"They see a movie and... if something beautiful strikes them emotionally, or in a beautiful way, they say 'That was faked' or 'They did that later on the computer'.
"Not a single shot in this movie has a sky enhancement or a replaced sky or a replaced landscape. That is Devon, Dartmoor... it is pretty extraordinary country."
> Jurassic Park voted greatest Steven Spielberg film by Digital Spy readers
> Steven Spielberg and John Williams's Top 5 movie score collaborations
Move through our gallery of images from the UK War Horse premiere below: