Simplify the following text for a Grade 5 native English-speaking person.
Original: In the northern part of the Great Barrier Reef , ribbon reefs and deltaic reefs have formed ; these structures are not found in the rest of the reef system .
Simplified: In the northern part of the Great Barrier Reef , there are ribbon reefs and deltaic reefs . These kinds of reef are not found in the rest of the Great Barrier Reef system .