Simplify the following text for a Grade 11 native English-speaking person.
Original: Until the 1960s there were some in the city center such as Humber Dock which became Hull Marina and Junction Dock which is now the site of Princes Quay shopping center . The Old Dock was filled in and is now Queens Gardens , St Andrews Dock was closed off and silted up ( some of it is now a retail park ) , the Victoria Dock closed in the 1980s and is now a housing estate , the Railway Dock closed in the 1960s and was later used as an extension to the Hull Marina .
Simplified: The dock closed in 1968 , part of the dock still exists , but without a lock connection to Humber dock ; the Princes Quay shopping center ( 1991 ) was built over part of the dock on stilts , the dock now features a fountain .