Many of Europe's freshwater fish and molluscs are now threatened species, a new EU study shows.
The European Commission called for urgent action to preserve the diversity of Europe's wildlife.
Pollution, overfishing, habitat loss and alien species are blamed for the decline in species.
The latest findings are based on a study of some 6,000 species for the European Red List - an assessment of threats to wildlife.
The list of Europe's threatened species includes 44% of all freshwater molluscs, 37% of freshwater fish, 23% of amphibians, 19% of reptiles, 15% of mammals and dragonflies and 13% of birds.
The Commission says 467 plant species are also under threat, including wild varieties of crops such as sugar beet, wheat, oats and lettuce. Such species are "vital for food security yet are often neglected in terms of conservation," the Commission says.
The Commission has urged the 27 EU member states to adopt sustainable farming and forestry methods to halt biodiversity loss.
Nature's 'goods and services'
"The well-being of people in Europe and all over the world depends on goods and services that nature provides," said EU Environment Janez Potocnik. "If we don't address the reasons behind this decline and act urgently to stop it, we could pay a very heavy price indeed."
There are some notable successes however for wildlife conservation in Europe.
The EU's Natura 2000 conservation network of protected wildlife areas aims to give endangered species a better chance of survival. Corsica's Centranthus trinervis plant and the land snails on Madeira are showing signs of recovery, the Commission says.
A biodiversity expert at the environmental group Friends of the Earth, Paul de Zylva, says the thriving otter population in the UK is also a success story - a sign that the healthy fish they prey on are abundant in once-polluted rivers.
But many of Europe's water species are suffering, often because their natural habitat is disappearing, he told BBC News.
"Our water resources are a symbol of whether we are getting environmental policies right," he said.
Threat from aliens
Invasive species from other parts of the world often spread through Europe's rivers, he said. Among them are Chinese mitten crabs, Himalayan balsam and Japanese knotweed. Rivers disperse plant seeds across borders - one reason why co-ordinated European action is necessary, he said.
It is vital for the EU to provide the right financial incentives for farmers to boost nature conservation when a revised Common Agricultural Policy takes effect after 2013, he said.
The Natura 2000 network was expanded this month, taking in an additional 18,800 sq km (7,259 sq miles) - most of that being marine areas.
The UK has added some biodiversity hotspots in the Atlantic, including reefs off Rockall Island.
In the Mediterranean, marine habitats of endangered turtles and monk seals have also been added to the list of more than 26,000 European conservation sites.
Source: BBC News