Dredging could continue until August under the current licence
Divers have raised concerns about the effect of thousands of tonnes of dredged waste on the environment off the Cornish coast.
About 49,000 tonnes of waste dredged from Millbay Dock in Plymouth is to be dumped at Whitsand Bay off Cornwall.
The dredging is part of a multi-million pound redevelopment of the area.
Divers say the dredging could affect the area's wildlife while regulators say there will be careful monitoring of the effects.
Diver Dave Peake said: "This is very unfortunate for the people who love Whitsand Bay, in particular, divers, anglers, fishermen and beachcombers.
"They will be seriously affected."
The Marine Management Organisation said there would be careful monitoring of the sediment depth while dredging took place.
It said some contaminants had been found, and material dredged between 1m and 2m deep could not be deposited at sea.
Instead, it must be treated before being used as part of the construction process at Millbay Dock or elsewhere.
Whitsand Bay, which is also used as a silt dumping ground by the Ministry of Defence, is about 1,000m from the Scylla wreck which is a popular diving spot.
The frigate was scuttled in Whitsand Bay in 2004 to create an artificial reef for divers and sea life.
Two divers were said to have died after becoming disorientated by silt on the Scylla, an inquest in 2009 was told.
Millbay's 15-acre harbour-side area is being redeveloped at a cost of £335m.
Lead developer English Cities Fund (ECf) has a licence to dredge and dispose of marine sediment from Millbay until 16 August.