The sea is really salty. You wouldn’t want to drink it! Some seas are saltier than others, and that’s why we find different fish in different seas. But, why is it so salty? This is one of those questions, where if you have a good think, the answer makes sense.
The sea gets its salt from two places. The land has lots of minerals/salts in it. When the slightly acidic rain falls onto the rocks, it starts to erode or dissolve, and the minerals get washed into streams, then into rivers and then into the sea. (It’s part of the water cycle.)
The other place the sea gets its salt is from the seafloor itself. The sea is covered with hot areas which tend to run along the edge of the tectonic plates. The seabed vents itself of heated water, and in the heated water, we find (you’ve guessed it) – salt.