Complex sentence: The Perth metropolitan area has two major river systems: the first is made up of the Swan and Canning Rivers; the second is that of the Serpentine and Murray Rivers, which discharge into the Peel Inlet at Mandurah.
Split into simpler sentences: The Perth metropolitan area has two major river systems; the first is made up of the Swan and Canning Rivers. The second is that of the Serpentine and Murray Rivers, which discharge into the Peel Estuary at Mandurah.