He is the one who has set free the two kinds of water, one sweet and palatable, and the other salty and bitter. And He has made between them a barrier and a forbidding partition.
~ Qur’an, 25:53
This is simply not true. Muslims usually lie about this. You can easily check for yourself if this is true. Rent a small boat. Take it to the mouth of the river. Taste a sample of the water. Keep moving further out to sea tasting samples. If the Qur’an is correct, the samples should taste perfectly fresh, then suddenly taste fully salty. If I am correct, and the waters do mix, then the samples should gradually get saltier and saltier.
If you think about it, the notion of not mixing is preposterous. At the mouth of every river would have to be an enormous pool of fresh water, all the water that had ever flowed down the river since the beginning of time. There would not be any room left in the oceans for salt water.~ Roedy (born:1948-02-04 age:68)