The Airports Commission has three options for runway expansions, two of which are at Heathrow, but nothing will happen before the election.
More than 700 seals have been spotted in the Thames Estuary in the first ever count carried out by air, land and water.
Clues on the future of airports in the south may be revealed today, including whether new runways or airports will be built.
Britain's biggest aviation union, Unite, has welcomed Sir Howard Davies' interim report on airport expansion but stated that a move away from a single hub airport would put jobs at risk.
The Airports commission has recommended runways to be built at Gatwick and Heathrow.
The commission left out Boris Johnson's proposal of a new airport on an artificial island in the Thames Estuary although it is being considered before the final report is due in 2015.
Unite's officer Oliver Richardson said: "We welcome Sir Howard Davies’ positive approach to airport expansion but any option which involves a move away from a single hub airport would damage the UK’s competitive edge and hit aviation jobs. "
– Oliver Richardson, Unite national officer
Losing a single hub airport would lead to global businesses reassessing their presence in the UK. Employers could relocate their European headquarters to other European nations like France and Germany which maintain single hub airports in Paris and Frankfurt. The Airports commission has also made the wise decision to kick Boris Johnson’s hare-brained ideas into the long grass. We can now get on with the serious business of devising a workable plan for airport expansion to support jobs and the UK economy."
The Davies Commission into the future of airports in the South highlighted the environment damage an airport in the Thames Estuary would cause.
The RSPB has said how the tidal mudflats and saltmarsh that line the estuary are one of the most important wildlife habitats in Europe.
In this morning's report, Sir Howard Davies favoured new runways at Heathrow and Gatwick ahead of the Thames, which he acknowledged to be expensive and environmentally damaging.
Chris Corrigan, the RSPB’s London and South East Director said:
“The RSPB, the people of North Kent and South Essex and a growing coalition of concerned groups won’t rest until the estuary is safe from unsuitable development. The spectre of an airport being built in this important landscape has haunted us all for more than 60 years.
“The massive loss of wildlife is just one reason why proposals like an estuary airport should never be allowed. Long established communities must be listened to and the unique landscape of marshes and Saxon churches which inspired Dickens and others must be treasured for future generations."
Of the three options for expansion presented by Heathrow Airport Ltd in the summer, the Airports Commission is only progressing one of them: the plans for a new runway to the north west of the existing airport.
The other Heathrow idea being investigated by the Commission comes from a pressure group called Heathrow Hub: the extension of one of the current runways.
The proposal is to build a third runway to the north west of the existing airport. It is a different proposal to the one approved by Gordon Brown when he was Prime Minister.
The new runway is further to the west - and anyone who knows this area will work out it brings the runway of Britain's busiest airport into conflict with Britain's busiest motorway, the M25. Look at the plan and you will see the runway is built over the top of the motorway.
That is not unusual. At Paris' Charles de Gaulle airport, a motorway passes under one of the runways in a tunnel. But it does mean this option is not cheap.
The Commission report's findings mean the village of Sipson near Heathrow Airport could later be affected if the original plans to extend the runway is supported.
Heathrow's bosses say their runway plan on a site to the north west of the airport - now on the Davies' shortlist - will mean less noise.
Local groups say the north west plan will require significant demolition in the villages of Longford and Harmondsworth and anti-Heathrow expansion group Hacan vowed today to fight the Heathrow plans.
However airlines, as well as the CBI and the London Chamber of Commerce, welcomed the commission's report.
The chief executive of London Gatwick airport has said he is 'very pleased' that Gatwick has been recognised in the shortlist.
Chief executive Stewart Wingate said: "Expansion at London Gatwick can give the country the economic benefits it needs."
"It is the only option which can the deliver the right type of capacity for the UK as it is the only airport serving all airlines models including both low cost and legacy airlines as well as both transfer passengers and people flying direct.
"I welcome the growing local support over the last year for our proposals. We do not take any of it for granted and we will do everything we can to engage with local people in the months ahead - including formal consultation on our proposals in the spring.
"The real debate starts now, not least on the environmental impacts and business case of each option. There is a lot of hard work ahead and intense scrutiny ahead but we are confident that by Summer 2015 there will be a wide recognition that expansion at Gatwick is the right choice for the future.”
Delighted proposal for a 4-runway airport near Abingdon has been rejected by the Airport Commission: http://t.co/evRJNE2Phb
The Board of Airline Representatives in the UK (BAR UK) say narrowing the options of developing the UK's future airport capacity to Heathrow and Gatwick is welcome news.
The chief executive of BAR UK said: "Despite the inevitable challenges and disagreement that will follow, the vast majority of airlines believe that expanding Heathrow is now the only sensible way forward for the UK.
"Sir Howard and his team have correctly identified that other proposals would cost billions in public funding and could create mass relocations and associated social upheaval and economic pain, or not deliver on the core objectives."
– Dale Keller, chief executive of BAR UK
Unlike rail, it’s the world’s airlines and their customers who will ultimately pay for the new airport infrastructure through airport charges. The travelling public want the industry and the Government to reduce delays caused by congestion and to fully meet their future travelling needs. This can only be achieved by having three or more runways together in the right location.
Medway Councillor Rodney Chambers explains his reaction to the announcement of runway expansions at Gatwick and Heathrow in the Airports Commission report this morning.
Davies Commission estimates cost of an estuary airport would be £82-112 billion: over 5 times cost of other options