150 species of animals and plants are under threat in London according to a report out by Natural England.
Otters have been sighted in London's rivers but remain under threat
Species include the otter, dormouse, skylark, southern wood-ant and the Chamomile plant.
The countrywide report, Lost Life: England's Lost and Threatened Species, also identifies species that have become extinct in London.
In recent years the capital has lost the green-winged orchid and the sea clover, a type of seagrass.
Other familiar species are also in decline - including the house sparrow, hedgehog, and European eel.
Reasons include loss of habitat, bad management, pollution and pressure from foreign species.
Among the 150 under threat 85 have been identified as a 'primary concern' by the London Biodiversity Partnership.
This includes plants, fungi, invertebrates and vertebrates.
Hedgehog numbers are in decline in the capital
Alison Barnes, Director of Natural England in London, said: "Coinciding with the International Year of Biodiversity, this report is a powerful reminder that we cannot take our wildlife for granted and that we all lose when biodiversity declines.
"With more and more of our species and habitats confined to isolated, protected sites, particularly in urban areas, we need to think on a much broader geographical scale about how we can reverse the losses of the recent past, climate proofing our natural environment, creating a network of natural green space in the city which will help to secure a more solid future for our wildlife."
The report identifies nearly 500 animals and plants that have become extinct in England - practically all within the last two centuries. It lists nearly 1,000 native species that have been given conservation priority due to the threats they face.
London's winning wildlife
However, it is not all bad news for London's wildlife.
Less than 60 years ago the River Thames was biologically dead due to excessive pollution. Now the river has dramatically improved and is home to 121 different species of fish and over 170,000 birds which have returned to live and breed in the estuary.
Peregrine Falcons have been breeding in London
Peregrine Falcon numbers have increased to five breeding pairs when it was thought there were none in the capital. Otters, which remain as a priority species, have been sighted in London's rivers, and the adder population has now stabilised and can now be found in five sites across London.
Also returning to the Thames is the short-snouted seahorse and the Atlantic salmon. The seahorses have been discovered in the river during routine conservation surveys over the previous two years.
Natural England is working with a range of partners in the England Biodiversity Group to manage entire landscape areas and the ecosystems that operate within them.
Alison Barnes continued: "Current, targeted conservation programmes have been central to supporting London's biodiversity and they show that we can reverse some of the losses of the past. But fire fighting to rescue species and habitats in severe decline can never be a long term solution. We need a step-change in conservation which focuses on restoring the health of ecosystems across the capital."
'We have to enhance and connect our city's green spaces to give wildlife and habitats more room to thrive. Only through co-ordinated activity across sectors can we reverse continuing declines in biodiversity in London.'
Natural England will present the data to an audience of leading conservationists at the London Zoological Society on 11 March 2010.