This amazing phenomenon has been mentioned in Surah Al-Furqan.
Surah Al-Furqn is the 25th chapter of the Holy Quran. It is Makki, has 77 verses and is in the 18th and 19th Juzes of the Holy Book. It is the 42nd Surah revealed to the Holy Prophet (PBUH).
Furqan means what separates and distinguishes between the truth and falsehood. It is also one of the names of the Quran.
Surah Al-Furqan includes discussions about Tawheed (monotheism), the Resurrection Day, prophethood, and fighting idolatry. In the final verses, it elaborates on the characteristics of steadfast believers.
The Surah can be divided into three parts in terms of subjects:
In the first part it criticizes the logic of the Mushrikeen (polytheists), responds to the excuses they make to not accept the truth, and warns them about the divine punishment. As a lesson, it also relates parts of the stories of people who lived before and faced severe punishment for opposing the messengers of God.
In the second part, proof is presented for Tawheed and some signs of God in the world are mentioned, from the light of the sun to the darkness of the night, blowing f winds, rain, revival of land after raining, creation of heavens and earth in six days and creation of the sun and the moon and how they move in their own orbit.
Among the issues mentioned in the Surah as wonders of creation is the one in verse 53: “It is He who has joined the two seas; one palatable and sweet, the other bitterly salty and has established a barrier between them as a partition.”
Verse 19 of Surah Ar-Rahman and verse 61 of Surah An-Naml also talk about the two seas. With the features mentioned in the Quran about the two seas, it can be said that it refers to a place where the Baltic Sea and the North Sea meet near Skagerrak.
The third part of Surah Al-Furqan elaborates on the characteristics of the steadfast believers and true servants of God as opposed to the unbelievers who always seek excuses. Some of the characteristics of the believers mentioned in the Surah include good beliefs, good deeds, resisting worldly desires, having commitment and social responsibility and having awareness.