According to the Office of Naval Research web site, the sea is salty for several reasons. 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. Minerals from the ocean's floor also dissolve into the water and add to the salinity, or salt content, of the sea. Oceans average about one cup of salt per gallon of water. That is why the sea is very salty.