53 bales of cannabis with a street value of around £9 million were retrieved from the sea by Customs last week.
During a routine morning patrol officers aboard a Customs vessel officers spotted suspect packages floating in the sea on the east side.
Two more vessels were called out and around two tonnes of cannabis were retrieved.
The matter is being investigated.
Collector of Customs John Payas says this is a significant seizure of drugs and a testament of Customs to disrupting drug networks.