Simplify the following text for a Grade 8 native English-speaking person.
Original: A build up of water in the Upper Bay allowed the river to break through to form the Narrows less than 12,000 to 13,000 years ago as it exists today ( see ; Waldman , 2000 ) .
Simplified: A build up of water in the Upper Bay allowed the river to break through to form the Narrows less than 12,000 to 13,000 years ago as it exists today .