Surah 25:53
"He (it is) who has let loose the two seas, this one sweet and fresh, and this (other) one salty (and) bitter, and placed between them a barrier, and an absolute ban."
Permanent Barrier between Fresh and Salt Water
When a fresh water river flows into the sea or ocean, there is a transition region in between. This transition region is called an estuary where the fresh water remains temporarily separated from the salt water. However, this separation is not absolute (thus cannot be described as a "barrier"), is not permanent, and the different salinity levels betw...