In the Quran, there are several verses that refer to the separation of fresh water and salty water in the seas. One such verse is:
“He released the two seas, meeting [side by side]; Between them is a barrier [so] neither of them transgresses.” Surat Ar-Raĥmān (Quran 55:19-20)
This verse suggests that there are two types of seas or bodies of water that meet but do not mix, with a barrier between them. Some scholars have interpreted this to mean that the fresh water from rivers and rainwater meets the saltwater of the oceans, but does not mix with it due to differences in density and salinity.
Another verse that touches upon this topic is:
“And it is He who has released [simultaneously] the two seas, one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition.” Surat Al-Furqān (Quran 25:53)
This verse implies that there is a boundary between the fresh and salt water in the seas, and that this boundary has been set by Allah to make it easier for humans to find sustenance in the sea.
Another verse regarding topic is :
“And the two seas are not alike: this, fresh, sweet, good to drink, this (other) bitter, salt. And from them both ye eat fresh meat and derive the ornament that ye wear. And thou seest the ship cleaving them with its prow that ye may seek of His bounty, and that haply ye may give thanks. ” Surah Al-Fatir (Quran 35:12)
Overall, while the Quran does not provide detailed scientific explanations of phenomena, it does refer to the separation of fresh and salt water in the seas, which modern science has come to understand as the result of differences in density and salinity.
Due to the different densities of the two types of water, they do not mix in the sea. Because it is less thick than saltwater, freshwater has a tendency to float on top of the latter. A clear separation between the two types of water can be seen in estuaries, which are areas where freshwater rivers and the sea converge.
Additionally, marine habitats may be significantly impacted by the mixing of freshwater and saltwater. For instance, if excessive freshwater reaches a coastal or estuarine location, the water’s salinity may decrease, harming marine life that is evolved to surviving in saltwater settings.