Instead, in went on to become the biggest ever animated film in the US, overtaking the Lion King.
Andrew and Lee said they were really pleased with the movie's underwater scenes.
"The thing we conquered the most was the cinematic trick of making you think you were underwater - something disappearing in the murk, shafts of light, plankton in the water," they said.
Finding Nemo was produced by the same people behind Toy Story, A Bug's Life and Monsters, Inc.
The directors say they're not ruling out a sequel.
"After Toy Story came out, everybody said 'Is there going to be a sequel?' We all said 'No way!' But you never know - maybe we will do Finding Nemo 2!"