The Strait of Gibraltar is a strait that limit the African continent and Europe. At Strait meetings 2 sea i.e. the Mediterranean Sea and the Atlantic Ocean. The second meeting of the flow does not cause the water to mix, but both are clearly separated according its origin respectively. The water of the Mediterranean Sea is colored dark blue water of the Atlantic Ocean and colored bright blue. If observed carefully, the two encounter a current divider creates an impenetrable to a depth of 1000 meters.
This phenomenon occurs because of the difference of ocean currents that move and tend to maintain the State of origin. In addition each of the surface tension of water creates an illusion as if there is a partition that separates the two so that the sea water not mixed.