Some of the most important special effects in the film are the smallest. In terms of the realistic look of the objects in the film, the particulate matter in water falls into this category. The filmmakers had to recreate the look of millions of tiny particles that are always present in ocean water, plus simulate light filtering away into the distance -- or murkiness. These unique attributes of the animated ocean needed to not only be included in most scenes in the film, but also to interact with the characters.
As light filters from the surface of the ocean to the bottom, different caustic lighting patterns are created. The artists on "Finding Nemo" not only had to recreate these shafts of sunlight, but also the light patterns on the uneven bottom of ocean. Additionally, filmmakers had to recreate the particular reflection of the inside of a fish tank from various angles.
Another area that required special attention was the constant movement of the ocean. Termed the "surge and swell" by the filmmakers, technical teams on the film greatly expanded their current simulation program to be able to handle the new environment. Programmers took the Pixar written simulation program "Fizt" (which controlled the fabrics and hair in "Monsters Inc."), and greatly expanded it. This new version was called "Splasht" and allowed simulated environments (for example, the ocean) to interact with themselves.
Unlike the nonliving sets in previous Pixar films, the filmmakers wanted to recreate the liveliness of a real coral reef in "Finding Nemo." The set designers and animators had to simplify the organisms that live in reefs, then design caricatured versions that would visually suit their needs. The films modelers were then required to populate the reef with different textures and colors, though much of the different moods were achieved through different lighting techniques.