Growing up, I learned that the brook running past our house in the middle of England flowed into the River Cherwell, which flowed into the Thames, which flowed to London and the sea. I dreamed of lowering a homemade canoe or coracle into the stream and making my way by water to the centre of the city. After graduation, a friend and I walked from London to Oxford along the Thames, past Hampton Court and the East Molesey reservoirs into a region of eyots, weirs, weeping willows and riverside pub gardens, almost 100 miles before the spires rose in the distance.
I knew little of the Thames to the east of the city, and for years I'd wanted to follow the river out of London towards the estuary. Since 2001, an extension to the official Thames Path has led from the gleaming steel hoods of the flood barrier at Charlton to the Dartford Marshes, close to the M25. I wondered where the grey ended and the green began.
Mid-July. High tide at the flood barrier. A man in shorts, sunglasses and straw hat (shirtless, medallion) was sitting on a bench, earbuds in, crooning Al Green's "Let's Stay Together" as he threw bits of white bread to the pigeons, Canary Wharf shimmering in heat-haze behind him. I set off past walkway benches under limes and poplars, past six women in saris chatting in the shade of a whitebeam, the smell of buddleia flowers complicated by wafts from the Tarmac plant. The river already had Amazon breadth, and the Tate & Lyle factory on the northern bank was a low skyline of chimneys, silos and gantries. Cranes chose prizes from scrap-metal hills. McCoy's and Lafarge trucks crammed the Woolwich ferry.
I was walking with the tide—you could see it withdrawing from the city, dragging past barges and yellow steel buoys bobbing like mines, mudflats glistening in front of the sewage works at Crossness. A mad day to be walking: the thick of a heatwave, hottest day of the year. At noon the air seemed a solid quantity I had to shoulder my way through, until slips of benevolent cooler air came in off the Channel like currents in water. Black-headed gulls ransacked the mudflats (a square metre of Thames Estuary mud can hold 1,200 worms) while gangs of starlings picked over exposed rocks. To the north, an acreage of new cars gleamed in the Dagenham compounds.
Often I had the path to myself. Two cyclists cruised past sucking at Calippos. Three men rehearsed their swings on Astroturf squares in a golf driving range. And there was strangely little movement on the river: just a squat orange tug shunting a barge eastwards, three swans off Jenningtree Point, a pair of crested grebes, a cormorant flying low above the water, as if avoiding radar. The sun gathered mirage-force as I pressed east past hangars, sheds and depots, until by the Conway asphalt plant I might have been dreaming the diesel chug of trucks and diggers, a steel clangour in the yards of trading estates.
The heat was a trial now, 33 degrees. But the walk was never boring. Here was the Thames Bubbler, one of the river's two oxygenation vessels, a massive blue-and-white barge, ready for action when sewage storm pipes overflowed and the river's oxygen levels fell; here too the new Riverside Resource Recovery facility in Belvedere, which processes 670,000 tonnes of waste from across London each year, most of it arriving on barges, turning it into enough electricity to power 100,000 homes. I walked out on the grand pier at Erith, where dozens of workers were eating lunchbreak picnics on benches raised high above the river.
East of Erith, the green began: reed beds round the yacht club, the path continuing on a raised dyke across Crayford Marshes. Canary Wharf was out of sight now. Three men roared past me on speedway bikes, silence and stillness closing in behind them. A few gaunt horses stood among clumps of ragwort. Lapwings and gulls rested motionless on the mud flanks of the River Darent, as if even birds were stunned by the heat. The Littlebrook power station and the long cable-stayed span of the Queen Elizabeth II bridge loomed beyond the Dartford Marshes.
A kestrel flew over the marshes. Then something else passed across the O of my binoculars: not a bird, but a model aircraft; I could see the pilots on the Dartford side, huddled round a transmitter. The kestrel and the model plane crossed each other's flight paths in front of the power station and the harp-string rigging of the bridge. I'd walked 15 miles. I thought of the river's journey from Oxfordshire and Gloucestershire. Maybe it was the heat: I was singing "Let's Stay Together" as I followed the River Darent into Crayford to catch the train at Slade Green.