text: why are the oceans salty and rivers not, what keeps them separate?   the rivers are not salty because an important source of their water is rain, which does not have salt.  but the water that runs through the land picks up dissolved salts and carries it to the ocean, where it accumulates over time.  that is the water that evaporates off the surface and becomes the rain that falls on the land to feed the rivers.  the salt does not evaporate, and is left behind in the ocean to accumulate.  so the salt from the land is gradually transferred to the ocean by the rain and by rivers that run to the ocean, etc.