Allah is great for all his gifts, have we ever wondered how the two kinds of water are in one place, but the water can not mix,,,??
the answer for us Muslims is in the Al-quran letter of Ar-rahman which means:
"He left the two oceans flowing, the two of them later met, between them there is a limit not surpassed each (Ar-rahman 19-20)".
Thanks to all my friends and steemiat and follow me, please 
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From @fuadz