truth of the Qur'an "two different seas are not mixed"

Allah subhana wata'ala says which means: He lets two oceans flow both of which then meet. Between the two there is a limit that is not surpassed by each. "(Surat ar-Rahman: 19-20)
in addition there is a river whose water is not mixed with salty sea water, there are also two seas that are also not mixed. The two oceans have different solute concentrations that appear to be different colors. This phenomenon occurs in the strait that separates between the African continent and the European continent. The strait is the strait of Gibraltar located in the country of Morocco and Spain