The confluence of Rio Negro and Rio Solimões, barely 10km from Manaus, is a popular tourist destination, because it is here that the Amazon River officially forms, but also because this "meeting of the waters" occurs in an astonishing way. Rio Negro has blackish water, with a high acidity level, whereas Rio Solimões is a so-called "white" river, laden with silt, with a neutral pH; the result is that their waters don't mix immediately. Over more than 10km the black and white currents remain separate, like oil and vinegar.