Germaine Greer: Your airport idea doesn’t fly, Boris Johnson

Take Two Tree Island, 640 acres of land on the other side of Ray Gut from Leigh-on-Sea, less than five miles across the water from the Isle of Grain. Around the island, which for most of the last century was a sewage farm and a rubbish dump, there are dense beds of sea grass. Sea grasses stabilise the sea floor, slow currents comb detritus and larvae out of the water flow, and provide nurseries for fish, shellfish, crustaceans and an array of other creatures. Seagrass beds are among the most biodiverse habitats on earth, but everywhere they are in trouble. Between them, Two Mile Island and Maplin Sands are hosts to the largest surviving continuous population of eel grass (Zostera noltii) in Europe.

These days Two Tree Island is a nature reserve, and the locals care about it. They care about it so much that they got together to stop the egg thieves who came year after year to rob the nests of the island’s avocets. Now, of course, it is aircraft they must worry about. Grain, and a mid-river site nearby at Shifting Sands, are currently being suggested as possible sites for a proposed new international airport which carries, for now at least, the name of “Boris Island” after Boris Johnson, the Mayor of London.

We don’t know whether an airport so close will disturb the avocets, or the wigeon and the Brent geese that feed there, and apparently we don’t care either. Boris’s brilliant wheeze can hardly be cancelled because of a few avocets. Or for a few plants like Least lettuce or bulbous foxtail or salt marsh goosefoot, or golden samphire. As for the invertebrates, only the insect charity Buglife could care about the rare beetles and bugs, weevils and horseflies that can live only on the three Ramsar wetlands in the estuary.

As far as most people are concerned, the Thames Estuary is simply the place where the muddy river dumps its sludge in the murky North Sea, the end of a drain carrying London’s dirty water. Drains are made to be built over, so we might as well park an airport over this one.

It’s not as if the Thames were the Grand Canal or even the Rhine. There’s no marvellous maze of jogging and cycling tracks, no chain of playgrounds, parks and gardens, very little to bring the citizens to the riverside. No carnivals. No regattas. What most people don’t know is that the Thames is now one of the cleanest metropolitan rivers in the world, and one of the most biodiverse, with 121 species of fish and untold numbers of marine invertebrates.

This pleasant situation is down not to good luck, but to hard work. The process began with the building of the London sewer (which eventually replaced the sewage farm on Two Tree Island) and continued with the improvement of water treatment technology at Beckton.

Originally the raw sewage was discharged straight into the Thames, but now the water is so clean you can drink it. You probably do. The Beckton sewage treatment plant at the end of the Northern Outfall Sewer is one of the biggest in Europe and set to get a whole lot bigger.

Thames Water is now upgrading the treatment plant to cope with the increased flows expected from the Lea Valley Tunnel and the Hammersmith Tunnel. Meanwhile it has been joined by what is rather euphemistically called a desalination plant, which takes river water at low tide and cleans it. Two ships, the Thames Bubbler and the Thames Vitality, are kept on the Thames to pump oxygen through the water whenever severely polluted run-off from overflowing sewers enters the river. Eventually Beckton will deal with this too.

What should not be forgotten by the champions of Boris Island is that, despite the construction of a whole system of flood barriers, the Thames remains at risk of flooding. The sea level is rising because south-east Britain is gradually sinking, righting itself after being tilted upwards by the weight of ice in northern Britain during the last Ice Age. What is more, the groundwater level is rising. In its natural state a river system can absorb most impacts, through its bordering reed beds and marshlands, but if these are to carry out their role as buffer zones, they need to keep their soft mobile edges. Only two per cent of the banks of the Thames is still in anything like a natural state.

How an airport would complicate the case is anything but clear. Wildlife depends on the alternation of drowned, wet, less wet and dry. The Thames Estuary provides a haven for an estimated 170,000 overwintering wildfowl, which is a pretty good reason for not putting an airport over it, and not just because of the risk to the birds. Like the visitors to Southend in its glory days, the birds come for the mud, and the worms that live in it.

Downstream from the Thames Barrier, in the estuary proper, the prospect is dreariest, unless you like tank farms and power stations. Tilbury Power Station is a classic of its kind, as is the 17th-century fort that nestles in its lee. Here the river spreads itself out, carrying its stained plume past Cliffe marshes, past Holehaven and Canvey Island to Southend. At Erith you might notice the stumps of trees that grew by the river 5,000 years ago. No matter how calm and sleepy or dim and dingy an estuary may look, it is a dynamic environment, that affects and is affected by the currents and tidal movements of the entire marine system from the Atlantic to the Baltic. Attempts to control it will be at best futile and at worst catastrophic. On both sides of the estuary, there are huge sandbanks that are constantly being shifted, pulled up and down the coast. The ecosystems of the Thames Estuary are complex and interdependent, and require management. Hence the setting up of the Thames Estuary Partnership.

Most Londoners, possibly including the Mayor, have never heard of the Thames Estuary Partnership. It was set up in 2000 to work “for the sustainable future of our estuary’’. The partnership is a charitable company with a board consisting of representatives of the Environment Agency, the Port of London Authority and Natural England.

The management committee consists of representatives of University College London, the RSPB, Thames Water, Kent County Council and Essex County Council. It has core funding from the various concerned agencies but most of the organisations (and there are dozens) participating in its projects have to be self-financing. TEP has a cute logo showing fishes swimming in clear blue water. Every year the partnership holds an annual forum; last year’s, which took place on November 10, discussed the Thames Tunnel preferred route, opportunities for freight on the river, the progress of the Balanced Seas marine conservation project, how planning can be linked with biodiversity and how it can work together with community interests. Not a word about an international airport in the Thames estuary.

Through the 20th century, all kinds of people – experts, tradespeople, volunteers, schoolchildren, local authorities – worked to return what was a dead river to life, and they succeeded. When a team from the Zoological Society of London spent three years (2004-2007) recording sightings of marine mammals in the Thames from Teddington to a line drawn between Shoeburyness and Sheerness, 691 animals were observed. After a co-ordinated campaign to involve the general public, all kinds of people – tourists, birdwatchers, anglers, the river police, yachtsmen – reported their sightings of harbour porpoises, bottlenose dolphins, grey seals and harbour seals.

It is understood that dolphins and porpoises are showing signs of stress and reduced viability, and various international conventions have been imposed for their protection, none of them applying to the Thames Estuary. The professionals rejoiced that the public was becoming aware of the importance of biodiversity and looked forward to significant public support for the various Biodiversity and Habitat Action Plans . That was before Boris. The marine mammal survey of the Thames goes on, and the sightings continue, but for how much longer? How many of the animals seen in the Thames will soon be sick or dead?

Airports produce vast amounts of pollutants of various kinds; among the most damaging are the toxic wastes that accumulate on the tarmac and find their way into groundwater. Even supposing the run-off from the tarmac on Boris Island were to be carefully managed (a big ask in itself), there is no way of stopping the precipitation of burnt fuel residues into the shallow water of the estuary.

Of all possible sites for an airport, an estuary is the most vulnerable. Nice, Boston, Eilat and Singapore all have semi-offshore airports; Hong Kong and Osaka airports are built on offshore islands. In the case of Boston, since 2004 more than 6,000 gallons of hazardous materials have been spilt at Logan International Airport, which is nothing unusual. Now the clam-diggers who work the surrounding waters of Boston Harbour are finding thousands of putrid dead soft-shelled clams. The mortality among the clams has been noticed because they are a cash crop; the annihilation of a whole galaxy of other marine organisms has not been noticed at all. By now the toxins that killed those have entered the food chain, with results so far uncalculated.

Concerns about the environmental impact of airports are always expressed in terms of the health of the human population. There is no concern for the health of the planet, though this will be the same thing in the end. It is perhaps the bitterest irony that a new airport for London may become a necessity because Heathrow has become too big and too dirty to use without incurring massive fines for excessive pollution. As people become more aware of the consequences for their own health of air and noise pollution, the idea of building airports offshore becomes more attractive.

The environmental consequences may be less obvious to humans, but for a vast range of other earthlings, they are certain to be catastrophic. Once the toxic fallout from jet engines has entered and accumulated in the food chain, the Thames may become once more what it was less than 100 years ago, a poisonous sluice.

Have your say. Do the dangers of a new airport in the Thames outweigh the opportunities? www.telegraph.co/earth