Simplify the following text for a Grade 6 native English-speaking person.
Original: In 1871 the area from the Kiso Three Rivers in the north to present-day Tsu became AnÅ tsu Prefecture , and the area south of that became Watarai Prefecture .
Simplified: In 1871 , the area from the Kisosansen River in the north to the city of Tsu became AnÅ tsu Prefecture . The area south of Tsu became Watarai Prefecture .