There are a few things involved:
1- elements shot on chroma: a bunch of objects that rotate slowly and a few characters that are either simulating slow motion or are shot at a higher frame rate for true slow motion.
2- distortion- using the displacement filter with a displacement map the underwater distorted look was achieved.
3- color grading- the cool bluish tones that give the underwater hue.
4- additional objects, like pieces of cloth or newspapers can be created using a 3d distortion filter like Free Form.