When a freshwater river flows into the ocean, it forms an estuary. Contrary to the description of a strict, impassable barrier, the waters actively mix, and their salinity levels naturally homogenize through a transition zone driven by tides and currents. While differing densities cause a visible stratification gradient—a phenomenon easily observable to ancient sailors and pearl divers—they do not remain permanently separated. Furthermore, the concept of distinct sweet and salty cosmic oceans was a prevalent mythological trope in antiquity, prominent in Akkadian and Sumerian lore.