I have fished some reefs right north of Grand Isle.
My brother in law has a camp at Tahiti East and we go North past the first island and you will see some PVC pipes up there. There are always a lot of boats there too.
Another reef is right East of the ship channel. There were PVC pipes around this reef also.
Then a couple miles North of the reef on the East side of the ship channel, there is a big reef with a tower on it.
Look close on this chart and you can see some of them.
http://www.charts.noaa.gov/OnLineViewer/11358.shtml