Simplify the following text for a Grade 5 native English-speaking person.
Original: The three islands have been declared a national park in 1980 , which was later extended to include the surrounding marine area and a section of Flores in 1984 .
Simplified: The three islands were named a national park in 1980 , . The park was extended to include the nearby parts of the ocean and a part of Flores in 1984 .