Simplify the following text for a Grade 5 native English-speaking person.
Original: The Abukuma River , with a length of 234 km , is the second longest river in the TÅ hoku region of Japan and the 6th longest river in Japan .
Simplified: It has a length of 234 kilometers . It is the second longest river in the TÅ hoku region of Japan and the 6th longest river in Japan .