It is He Who has let free the two bodies of flowing water: one palatable and sweet and the other salt and bitter; yet has He made a barrier between them a partition that is forbidden to be passed. 3111 3112
Maraja: literally, let free or let loose cattle for grazing. Bahrain: two seas, or two bodies of flowing water; for bahr is applied both to the salt sea and to rivers. In the world taken as a whole, there are two bodies of water, viz.,: (1) the great salt Ocean, and (2) the bodies of sweet water fed by rain, whether they are rivers, lakes or underground springs: their source in rain makes them one, and their drainage, whether above-ground or underground, eventually to the Ocean, also makes them one. They are free to mingle, and in a sense they do mingle, for there is a regular water-cycle: see n. 3106 above: and the rivers flow constantly to the sea, and tidal rivers get sea-water for several miles up their estuaries at high tide. Yet in spite of all this, the laws of gravitation are like a barrier or partition set by Allah, by which the two bodies of water as a whole are always kept apart and distinct. In the case of rivers carrying large quantities of water to the sea, like the Mississippi or the Yangtse-Kiang, the river-water with its silt remains distinct from sea-water for a long distance out at sea. But the wonderful Sign is that the two bodies of water, though they pass through each other, remain distinct bodies, with their distinct functions.
In Allah's overall scheme of things, bodies of salt and sweet water, which are adjoining and yet separate, have significant functions. Weaving a harmonious fabric out of these different fibres shows both Allah's power and wisdom. Incidentally, this verse points to a fact which has only recently been discovered by science. This fact relates to the oceans of the world: they meet and yet each remains separate for Allah has placed "a barrier, a partition" between them.