Experiment, Rivers, Seas and Oceans

Experiment about water density

Water in the rivers can be fresh or salty, depending where the river is and what are its water source. The main factor determining the freshness of the water in the rivers is the type of a water source from which it is fed.

In most cases, rivers are thought of as freshwater, in other words, they do not have significant amount of salt. Freshwater rivers are fed mainly by underground waters and precipitation and melting snow/ice.

Saltwater rivers are usually near the sea and are called an estuaries. Estuaries are places, where fresh river water meets the sea water. Sea water contains a lot of salt, mainly sodium chloride (kitchen salt) and other minerals. When river water flows into the estuary, its water becomes saline.

Here is a few examples of saltwater rivers (estuary) on different continents:

The Amazon river: In the estuary of the Amazon river, that flows into the Atlantic Ocean in South America, fresh river water mixes with sea water.

The Mississippi river: In North America, the Mississippi river flows into the Gulf of Mexico, where its fresh water meets the sea water.

The river Thames: In Europe, the river Thames flows into the North sea, creating salty estuary.

The Nile river: In Africa, the Nile river flows into the Mediterranean sea, where also is a salty estuary.

The Ganges river: In South Asia, the Ganges river flows into the Bay of Bengal, where one can find an estuary with mixed fresh-salty water.

The river Yancy:  In East Asia, the river Yancy flows into the East China Sea, where fresh waters meet with sea waters.

Try with kids finding the beforementioned rivers and their estuaries, where fresh water mixes with the salt water.

27.09 Dzien Rzek 2.1


  • Small plastic beads
  • Two glasses of water
  • Salt

Task flow

The teacher pours 2 spoons of salt to the one of the glasses and mixes until the salt dissolves completely. Now kids should wonder, what can happen, when they throw the plastic beads into both glasses. Will the beads sink or will they float on water?

One of the kids throws the beads into both glasses and the rest observes the changes. The salt should make it so the beads float on the water. Adding salt to the water causes it to increase in density. That means that it gets heavier. A lot of things, that sink in fresh water, float in salt water. The more salt, the more dense the water is and the more things will be floating on it.

Warning! Perhaps you will need to add more salt to the water, depending on the weight of the beads. It is the best to add so much salt that it stops dissolving. And there will be a white sediment on the bottom of the glass.

14.11 Dzien Czystego Powietrza 1 E1668703355599

This post was created as part of a project co-financed by Deutsche Bundesstiftung Umwelt in cooperation with Naturschutzzentrum Oberlausitzer Bergland.

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