The oceans and seas are normally saline, rivers belong to the fresh waters, lakes can be either fresh water, like most of them, but there are also some saline lakes. The most famous are the Dead Sea and Lake Retba in Senegal, which has the highest salt content of all lakes.
And now, back to the point: there is also a third class of lakes. Half saline, half fresh water. That's it, Lake Balkhash has two distinct parts, the western section is fresh water while the eastern section is naturally saline. The two parts are divided by a strait in the middle of the lake, and there is basically no water flow between the two parts due to the sensitive equilibrium of evaporation in the eastern basin and the drain of the western basin.