Complex sentence: The Ĳsselmeer is a freshwater lake fed through the Ketelmeer by the river IJssel, which gives its name, it is mainly fed by water from the Rhine since this river is branch of it.
Split into simpler sentences: The Ĳsselmeer is a freshwater lake fed through the Ketelmeer by the river IJssel, which gives it its name. It is mainly fed by water from the Rhine since the IJssel is branch of it.