The image above is nowadays being taught in the world major universities. It illustrates an established scientific fact in the field of hydrology. We see how the sweet palatable water of the river flows and mixes with the salty water of the ocean. Scientists discovered a barrier that is formed between the two waters. The barrier (isthmus) prevents the salty water from overwhelming the palatable water of the river.  Allah the Exalted revealed this scientific fact, 14 centuries ago, in the Quran as He says: 

(And He is Who has made two seas to flow freely, one sweet that subdues thirst by its sweetness, and the other salty that burns by its saltness; and between the two He has made a barrier and inviolable obstruction) [Al Furqan: 53].

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By: Abduldaem Al-Kaheel