He is the One who merges the two bodies of water. This is fresh and palatable and this is salty and bitter. He made between them a partition and an inviolable barrier.
Translation endnotes
[25:53] Could this barrier be evaporation? The water of lakes is maintained by rain. Through evaporation, the salty ocean water is filtered from its minerals. Evaporation creates a physical barrier between salty water and drinkable water.