Complex sentence: Peneus River used to flow on what is now Andravida creek in ancient times and was a swamp region, but some torrential weather or a drought changed the course of the river to the Palaiochori.
Split into simpler sentences: Peneus River used to flow on what is now Andravida creek in ancient times and was a swamp region. Some torrential weather or a drought changed the course of the river to the Palaiochori.