Developers say ecological surveys are under way in preparation for one of the world's biggest wind farms.
Wildlife campaigners want wind farms 'in the right place'
The Thames estuary was earmarked as a key site as early as 2003 and is expected to generate enough power to supply all of Kent and East Sussex.
Developers said on Tuesday electricity generation should be under way by 2008 if work continues as planned.
Councils have backed plans for offshore turbines in the estuary off Herne Bay, but opposed turbines on Romney Marsh.
The first two wind farms planned for the estuary were at Gunfleet Sands, off Clacton-on-Sea, Essex, and at Kentish Flats, off Whitstable and Herne Bay, with 30 turbines planned for each site.
Four more sites were later planned for the Thames estuary which were further offshore.
Maps show the largest of those sites, London Array, in the centre of the estuary.
The three smaller sites are Thanet, off the Kent coast, Greater Gabbard, off the Essex coast, and Gunfleet Sands II, an extension of the site off Clacton.
BBC South East Today has revealed that the largest site will be the size of 25,000 football pitches with 300 turbines sited there.
Gordon Edge, a spokesman for the British Wind Energy Association, said: "It is a legal requirement that the surveys are done.
"People are out there looking at birds and conducting seabed surveys."
Adrian Thomas, a spokesman for the RSPB, said: "A wind farm sited in the wrong place could be disastrous for some bird populations, so we would fight those as hard as we could.
"If we are happy that a wind farm is not going to have a really bad impact on wildlife, we will step back and allow that wind farm development to take place."