Barramundi fish (the silver fish in the reef schools): a real 3D model, "BarramundiFish", by Microsoft, shared under CC0 (public domain). Found in the Khronos glTF-Sample-Models collection: github.com/KhronosGroup/glTF-Sample-Models. I shrank its textures to save space.
Everything else (water, light, rock, coral, sponges, every other animal, the vents, the wreck and the trench) is built by code. These are 3D models made from simple shapes, so they are stylised, not photographs, and not exact in colour. Animals are shown at their real size and at the depths where they really live.
The places are real kinds of places found around Pacific islands such as the Marianas: a coral reef, the twilight and midnight zones, hydrothermal vents on an undersea volcano, the abyssal plain and a deep trench down to the depth of the Challenger Deep (10,935 m). In the real ocean they are tens to hundreds of kilometres apart; this dive puts them one after another. The shipwreck is imagined.
The descent is sped up, like a time-lapse. A real submersible takes about four hours to reach the bottom of the deepest trench; here the depth counter runs much faster, while everything near you is at real size and speed.
The sound is made live in your browser. There are no recordings.
Fonts: Fraunces and Figtree, SIL Open Font License, included with the site.
3D engine: three.js r186 (MIT licence), included with the site.