﴿ ۞ وَهُوَ ٱلَّذِى مَرَجَ ٱلْبَحْرَيْنِ هَٰذَا عَذْبٌۭ فُرَاتٌۭ وَهَٰذَا مِلْحٌ أُجَاجٌۭ وَجَعَلَ بَيْنَهُمَا بَرْزَخًۭا وَحِجْرًۭا مَّحْجُورًۭا ﴾

“AND HE it is who has given freedom of movement to the two great bodies of water – the one sweet and thirst-allaying, and the other salty and bitter - and yet has wrought between them a barrier and a forbidding ban.”

Please check ayah 25:54 for complete tafsir.