After watching the video that I have posted earlier, it is good to read up on the reasons given in the Quran for why different types of sea water do not mix. You may click on the link
https://www.islam-guide.com/ch1-1-e.htm
Although there are large waves, strong currents, and tides in these seas, they do not mix or transgress this barrier.
The Holy Quran mentioned that there is a barrier between two seas that meet and that they do not transgress. God has said:
He has set free the two seas meeting together. There is a barrier between them. They do not transgress. (Quran, 55:19-20)
But when the Quran speaks about the divider between fresh and salt water, it mentions the existence of “a forbidding partition” with the barrier. God has said in the Quran:
He is the one who has set free the two kinds of water, one sweet and palatable, and the other salty and bitter. And He has made between them a barrier and a forbidding partition. (Quran, 25:53)
I personally believe that besides signifying the greatness of Allah, the interpretation of the verses can go beyond the literary meaning. The message can be for humans, that is, do not transgress. We should be aware of the barrier. There are limits in everything we do.
Wallahualam.