Simplify the following text for a Grade 6 native English-speaking person.
Original: The upper Niger , from the source past the trading city of Timbuktu to the bend in the current river , once emptied into a now-gone lake , while the lower Niger started in hills near that lake and flowed south into the Gulf of Guinea .
Simplified: The upper Niger , from the source , past Timbuktu , to the bend in the river , used to empty into a lake , but the lake has now gone . However , the lower Niger started in hills near the lake and flowed south into the Gulf of Guinea .