David White, 42, and Kaye Moss, 43, ran out of air as they tried to find their way out of a small compartment on the HMS Scylla off Whitsand Bay in Cornwall.
They dived to the artificial reef and entered a room via a hatch but stirred up silt as they went in. The sediment made it impossible to see and they were unable to find the exit, an inquest in Plymouth, Devon, heard.
Both bodies were later recovered from the room, with Kaye's buried beneath the silt.
Thousands of tonnes of dredged material is dumped near the Scylla from the nearby Devonport Naval Base to keep the River Tamar clear for ships.
An MoD spokesperson confirmed that 40,000 tonnes of dredged material had been deposited at the site last year.
Despite being experienced divers with hundreds of dives between them, Mr White and Miss Moss failed to attach a safety line which could have lead them out of the wreck, the inquest heard.
The couple died during a trip with three other divers from the South Gloucester Sub Aqua Club on August 2, 2007.