The freshwater found in rivers originates from rainwater and melting snow/ice. As this water flows downriver towards the ocean (or sea), it picks up trace amounts of minerals (including salt) from the earth (rocks, wood, etc.) and eventually empties them into the ocean. The location where freshwater from rivers transitions into ocean saltwater is called an estuary. The water here is called brackish water.
As saltwater from the oceans evaporates, the salt molecules are left behind and accumulate over time, forming potent ocean saltwater. As this evaporated water in the atmosphere cools down enough, it condenses and eventually changes back into freshwater. When it rains, this freshwater falls back into the rivers, and this process repeats indefinitely.
So, river freshwater does have some salt in it, however, since the salt is continuously flowing into the oceans and not accumulating in rivers as it does in the oceans, the salt content is minimal and unnoticeable.
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- Rivers deposit an estimated 4 billion tons of salt into the oceans every year.
- The Pacific Ocean contains around 25,000 islands.
- The longest river in the world is the Nile River at over 4,000 miles.
- NOAA.gov – Why is the ocean salty, but rivers flowing into it are not?
- TweenTribune.com – Why are lakes freshwater and oceans saltwater?
- Science.co.nz – Fun Ocean Facts