When a River flows into the sea, where does the freshwater end and where does the salt water start?

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When a River flows into the sea, where does the freshwater end and where does the salt water start?

In: Biology

They meet in estuaries that have what is considered brackish water. It has a lower salt content than sea water but more than the fresh river water.

Estuaries are important ecosystems for many animals such as birds and fish along with many more.

[check this out](https://en.m.wikipedia.org/wiki/Estuary)

The answer varies by the river. In the extreme case of the Amazon, by far the largest river in the world, you can be at sea, out of sight of land, and still the water is fresh enough to drink. Most rivers are undrinkably salty well before they reach their mouth, especially as rivers tend to flow more slowly nearer the coast and tides can push sea water many miles inland. Faster flowing rivers in areas of small tides can have fresh water close to their mouths.

Living at the mouth of a large river, all I can say is that it varies.

– The water mixes so there isn’t really a line where it is completely fresh on one side and completely salt on the other.

– The fresh water floats on salt water so there are places where the top few inches are mostly fresh but the rest isn’t.

– The line (such as it is) moves in and out with the tide.

– The flow of the river changes greatly with the seasons. During freshet, more than twice as much water flows out of the river and the discharge plume is much larger.

– If the weather is rough, waves mix the water faster making it saltier closer to the river.

To try to put rough values on it:

Almost all of the Strait of Georgia is less salty than the Pacific Ocean mostly due to the Fraser river. The main plume usually extends at least 10km out at the surface and probably about 20 during freshet.