eli5: Why is water clear in small amount but blue in large amount like an ocean?

Question

I thought it might be the reflection from the sky but if that was the case, why does the ocean appears more blue the deeper you go?

In: 2918

Answer 1

This is the absorption spectrum of water.
https://www.researchgate.net/profile/Hrebesh-Molly-Subhash/publication/258384344/figure/fig23/AS:325110046183441@1454523683523/Water-absorption-spectrum-The-original-data-consult-from.png

Note that the absorption is higher in the red than in the blue. This means that the light remaining after passing through water will have more blue left in it than red in lt. And will thus appear blue.