Surah 55:19–21:
He released the two seas, meeting; Between them is a barrier so neither of them transgresses. So which of the favors of your Lord would you deny?
Verses 19 and 20 claim that God lets two bodies of water meet, but maintains a barzakh (a physical or metaphysical barrier) between them so that they do not mix or "transgress" over one another. This is widely cited in modern "scientific miracle" literature as a prediction of modern estuarine physics, haloclines, or the meeting of the Atlantic and Mediterranean.
The Scientific Error: Marine biology and oceanography completely contradict the claim that these waters do not mix. In reality, while different bodies of water may have varying salinities, densities, and temperatures, they actively and continuously mix through molecular diffusion, tidal forces, and upwelling. The water molecules constantly cross these transitions; there is no static, permanent barrier locking them in place.
The Mythological Source: To a historical critic, this verse is a monotheistic recycling of ancient Mesopotamian cosmologies. The Babylonian Creation Myth (Enuma Elish) famously describes the primordial world as the meeting of two water deities: Apsu (the sweet, fresh water) and Tiamat (the bitter, salty sea water), whose bodies touch but are separated by a cosmic boundary. The author of the Quran adopts this ancient, regional visual understanding of coastal estuaries (where freshwater rivers meet the sea) and attributes it to a permanent supernatural miracle, unaware of the actual mechanics of fluid dynamics.