Water is blue, just like air is blue, just like blue-tinted glasses are blue. They disproportionately absorb non-blue frequencies, which is what we mean when we call something "blue".

My bad! Should've said "water is wet" or maybe run my response through ChatGPT, maybe that'd have caught it and offered a replacement!

Not really - there are blue and blood red oceans, but you might never hear about it (there is a book about it and strategy worth to read).