Verses 54:19-20 are marketed as “miracles of the Quran” but are they? It is not two seas but fresh water from rivers mixing with sea, a process that is happening ALL the time but when the water is flowing too fast, it may appear they are not mixing. But let us see that the Tafsir says:
Interpretation of Ibn Katheer – that is, he made a barrier between fresh and salt water, that is: a barrier that prevents them from mixing.
First, as we are used to, all the information mentioned in the Qur’an is copying, pasting, and stealing from civilizations, cultures, and people who preceded Muhammad by thousands of hundreds of years, including Aristotle, the Greek philosopher who was a student of Plato. Aristotle says that salty water does not mix with fresh water that is suitable for drinking, because salty water is less than fresh water… Is Pagan Aristotle now a prophet and should we pray for Zeus?
From a historical point of view, there are those who mentioned the information hundreds of years before the Qur’an, and it is not new information.
Now we come to explain the phenomenon scientifically:
When fresh water and salt water meet at an estuary, they don’t always mix easily. Because freshwater flowing down an estuary is less salty and less dense than water from the ocean, it often floats on top of heavier seawater. The amount of mixing of fresh water and sea water depends on the direction and speed of the winds, the tidal range, the shape of the estuary, and the volume and rate of river water flow during the entry into the estuary.
Firstly, a well-known phenomenon at that time, and also scientifically documented, is not accurate because it is based on observation with the naked eye and Islamically contains an error because Muhammad’s interpretation of it is the existence of a barrier (isthmus) that separates salty and fresh water (and this does not exist).