The ocean is blue because water absorbs colors in the red part of the light spectrum. Like a filter, this leaves behind colors in the blue part of the light spectrum for us to see.
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The ocean? It feels like a good time to avoid it. - The Washington Post
Why is the Ocean Blue?
Is the ocean blue because it reflects the color of the sky? - Quora
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40 Ocean Facts That Will Blow You Out of the Water — Best Life
Why Is The Ocean Blue?, Rayleigh Scattering
Why Is the Ocean Blue?
Why Is The Ocean Blue?, Rayleigh Scattering