Allah says in Qura’an
He released the two seas, meeting [side by side];
Between them is a barrier [so] neither of them transgresses. (55: 19,20)
Rio Brazil, Negro River, to meet with the Amazonas forming the Amazon River. Where the two rivers meet the the clear black warm slow moving Rio Negro and the fast moving cold muddy Amazonas do not mix; they run for several miles before finally blending together as the Amazon River that runs to the Atlantic Ocean.