(Furqan) 25 : 53
وَهُوَ الَّذِي مَرَجَ الْبَحْرَيْنِ هَٰذَا عَذْبٌ فُرَاتٌ وَهَٰذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَحْجُورًا
And He is the One Who has set free two seas, one fresh and sweet and another salty and bitter, and He placed between them a barrier, an unseen partition that is forbidden to be passed.
It is told in verses 55: 19-21: “He has set free two seas meeting one another, between them is a barrier which they don’t transgress; then which of the favors of your Lord will you reject?” The Three-Time-Knower Lord has set an unseen barricade between freshwater and saline water of the sea which can be seen in many regions of the world. Shortly, man will be forced to take freshwater from such regions. See explanation 14: 34; 17: 41 and 23: 99-100.