What distinction does Mr. Patel make between the ocean and the swimming pool?

From the text:

When he felt that I had progressed sufficiently, we turned our backs on the laughing and the shouting, the running and the splashing, the blue-green waves and the bubbly surf, and headed for the proper rectangularity and the formal flatness (and the paying admission) of the ashram swimming pool.

Something about formal flatness and rectangular shaped or something like that