Simplify the following text for a Grade 6 native English-speaking person.
Original: It flows through the Midlands ( forming a once significant boundary between the north and south of England ) until it joins the River Ouse at Trent Falls to form the Humber Estuary , which empties into the North Sea below Hull and Immingham .
Simplified: It flows through the center of England until it joins the River Ouse to form the Humber which empties into the North Sea .