Of the main types of coral reef, this one is miles offshore with a channel between it & the mainland
[DOC] [TLE] Great Barrier Reef | reef, Australia | Britannica.com [PAR] Jul 22, 2016 ... Complex of coral reefs, shoals, and islets in the Pacific Ocean off the ... for more 
than 1,250 miles (2,000 km), at an offshore distance ranging from 10 to 100 miles 
... of coral sand, or cays; others fringe high islands or the mainland coast.