Thurrock Thameside nature park has the look of a classic wildlife reserve. Perched on the Essex coastline on the Thames estuary, it covers 120 acres of grass, bramble and shrub. It is home to barn owls, brown hares, harvest mice, great crested newts, yellow wagtails, reed buntings, adders and various orchids. It is, in short, a haven for nature lovers.

The site has one unusual feature, however: it rests on a thick bed of rubbish and domestic waste that has been dumped by six London boroughs over the past 50 years and which, in places, has piled up to form layers that are 30m thick. It is a strange bedrock for a nature reserve to say the least.

It is a certainly remarkable transformation. And yesterday, the Essex nature park – awarded an ethical award by the Observer in 2011 – was given a great accolade: Sir David Attenborough conducted the official opening. "We live in a crowded country and need to respect its limits to sustain us," he said at the opening ceremony. "Change like this must become the norm."

This point was backed by John Hall, chief executive of Essex Wildlife Trust, which has played a key role in turning the giant rubbish dump into a wildlife refuge. "This was an old gravel pit and once excavations were finished it was used as a vast dump for London's domestic rubbish," he said. "Every day, barges of the stuff were brought up the Thames and dumped. The only wildlife we had were gulls – thousands of them. They used to go through the rubbish for food. They would drag waste out then spread it round the area. Local people would find they had dropped rotting chicken bones in their garden."

It was a very different vision yesterday. Skylarks – whose numbers are declining alarmingly elsewhere – were singing while several adders were spotted by visitors. "Adders are very shy, which suggests there is now a healthy population at Thurrock," Hall said. "That in turn, indicates healthy numbers of their prey, creatures such as voles. The presence of these animals also explains significant numbers of peregrines and barn owls."

But creating this haven from a rubbish tip – carried out by the wildlife trust and the landfill company Cory Environmental – has not been easy. First the rubbish had to be compacted. Then a thick layer of clay, known as a pie-crust, was placed over this vast sea of waste. This has since been covered in soil on which grass, bushes and wildlife have established themselves.

"So far we have 120 acres fully restored," said Hall. "There are a further 400 acres we will take over once they have been covered with soil and plants. We also plan to take over some other local land so that we will have a reserve of more than 800 acres here in the near future, one of our biggest."

For good measure, the reserve is also generating power for the electricity grid. The methane created by the rotting foodstuffs at its core is collected and burned to drive 15 turbines that will provide enough electricity to power 100,000 homes for the next 30 years.