why is the Gulfstream dark blue?

I live in south Florida and fish alot. We leave out of Port Everglades and go straight out to the Gulfstream.The water is greenish until we hit the gulfstream,it changes from greenish to dark blue within 2-3 feet.It's not that the gulfstream is deeper because it isn't.
Answer:
It has a different temperature and different types and amounts of suspended particles, especially algaes, as compared to in-shore waters.

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How exactly is this question classified as "Medicine?"

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