He has let loose the two seas (the salt and fresh water) meeting together. Between them is a barrier that none of them can transgress. (Qur’an, 55: 19-20)

A FAMOUS French oceanographer, J. Cousteau, gives the following account as a result of his studies of water barriers.

“We studied the assertions by certain researchers about barriers separating seas and noticed that the Mediterranean Sea had its own salinity and density and housed autochthonous fauna and flora. Then we examined the water of the Atlantic Ocean and discovered features entirely different from those of the Mediterranean Sea. According to our expectations, these two seas that merged in the Strait of Gibraltar should present similar characteristics in terms of salinity, density, and other properties. The two seas presented different features even though they were adjacent. This greatly puzzled us. An incredible barrier prevented the two seas from coming together. The same sort of barrier had also been observed in Bab Al-Mandab in the Gulf of Aden connecting with the Red Sea.

Subsequent to our observations, further researchers made it clear that the seas which had different characteristics had some barriers.”

This fact that astounded oceanographers was revealed 14 centuries ago in the Qur’an. This aspect, not visible to the naked eye and appears to be in conflict with the properties of water known to man, was first revealed to men in the Arabian peninsula, men who were not at all experienced in any sense with oceanography.

The barriers between adjacent seas demonstrate a rich diversity, a result of the perfect planning of God. Wherever we turn our gaze, the complexion of human beings, the infinite diversity of flowers, etc., demonstrate the marvelous diversity of God’s creation. The Qur’an refers to the waters that do not coalesce. This is because of a physical characteristic called “surface tension.” Thus, neighboring seas present different densities, salinity rates, and compositions. These differences enable media that permit different species to coexist. Thus, fish, plants, and microorganisms living underwater present untold varieties. Water, which usually mixes easily, can turn into a wall thanks to God’s imposition and operation of physical laws, contributing to this variety. This fact is not affected by strong waves and currents. This property to which the Qur’an refers is a miraculous statement unknown at the time of the Prophet and presents clear evidence for the man of understanding.

He is the One who has set free the two seas; one is sweet and palatable, and the other is salty and bitter. And He made a barrier between them, a partition that is forbidden to be passed.
And it is He Who has let free the two seas (kinds of water): one palatable and sweet, and the other salt and bitter; and He has set a barrier and a complete partition between them. (Qur’an, 25:53)