Ар-Рахман 55:21

Allah created Different Types of Water

مَرَ‌جَ الْبَحْرَ‌يْنِ يَلْتَقِيَانِ (He has set forth the two seas that meet together...55:19). Literally, the verb maraja means 'to let loose'. The word bahrain [ two seas or two types of waters ] refers to sweet and salty waters. Allah has created two types of waters. In some places the two seas meet together, the samples of which are available in every region of the world. However, where the sweet and salty waters meet, there is a distinct barrier between the sweet and salty waters. In some cases, the two types of waters are seen distinctly in higher or lower position. If the salty water overrides the sweet water, the characteristics of the sweet water will not be spoiled; nor will the characteristics of the salty water be affected in any way if the sweet water overrides it. Thus the Qur'an states: مَرَ‌جَ الْبَحْرَ‌يْنِ يَلْتَقِيَانِ بَيْنَهُمَا بَرْ‌زَخٌ لَّا يَبْغِيَانِ He has set forth the two seas that meet together, while between them there is a barrier they do not transgress....55:20)