As rivers run toward the ocean, they pick up salt and other minerals from the rocks and sand they pass by. The rivers’ waters are constantly being replenished by fresh water from rain and springs so they don’t taste salty, but the water in the ocean collects all of the salt and minerals from all of the rivers feeding into it.
Minerals from the ocean’s floor also dissolve into the water and add to the salinity, or salt content, of the sea.
Since this has been happening for millions of years, the oceans now have a lot of salt — about one cup per 3.8 litres!
You can’t taste the salt in the river because rivers don’t contain high enough levels of salt at any one time. You can not taste it in the lakes because while one river brings the salt in, another rivers it out.