Pixelating the waves was quite a challenge, and took me some time to get a clue of how it could be done.
Initially I drew the top of the waves with small strokes, which are pointing towards the end of the wave where the wave falls apart.
I wasn't satisfied with the result, so I took another approach. This time I drew a sort of craquelure - which many old paintings have - on top of the wave and added a dithered transition from dark to light gray and vice versa.
I also noticed that the transition towards the falling apart of the wave
was too obvious, too hard, so I reduced the contrast.
Along with this adjustment, I added more contrast underneath the wave, so the contrast between the white water drops increases.
In this case, I didn't focus on every water drop/pixel separately, but concentrated on the overall look.