Natural habitats and threatened species could be at risk if the UK votes to leave the EU, North Norfolk MP Norman Lamb warned today.
It comes as the RSPB and World Wide Fund for Nature (WWF) join forces to say that Britain's environment is safer in Europe.
EU conservation laws give special status to areas like the north Norfolk coast, the Norfolk Broads and the Ouse Washes, protecting them from over-development.
More than 1,000 threatened species are protected by EU legislation. Some of our most endangered birds, including the hen harrier which has been spotted in recent years in Eastern England, benefit from EU protection.
'Being in Europe means strong, stable protections for our natural environment, both at home and abroad,' said Mr Lamb.
'These protect Norfolk's distinct landscapes from over-development and have supported the recovery of some of our most treasured wildlife.
'European agreements have also helped tackle international problems such as acid rain and pollution in our rivers and seas.
'Leave campaigners have made no secret of their desire to water down these vital environmental protections.
'We must not let them throw away all the progress that has been made in protecting our shared nature and wildlife.'
Mike Clarke, chief executive of the RSPB, said: 'We have always believed that, because nature transcends national boundaries, it needs cross-border co-operation to protect it and a common set of international standards that enable it to thrive. As the prime minister rightly points out, UK membership of the EU has benefitted nature and the environment in ways that would be hard to replicate if we left.
'The RSPB will not be telling people how to vote, and we recognise that voters will be weighing up a range of issues when casting their votes on June 23. However, we want a secure future for our most precious wildlife and the places they call home. In weighing up the current evidence, the uncertainties and the balance of risks, we have concluded that the safer option for nature is for the UK to remain a part of the European Union.'
David Nussbaum, chief executive of WWF-UK, said: 'The outcome of this referendum will have profound implications for our countryside, wildlife, rivers and seas. David Cameron is right to put the environment at the top of the agenda today, and he has highlighted the range of benefits that EU membership has delivered for our species and habitats.
'Nature doesn't observe national boundaries but still needs protection. So whatever the result on June 23, we must work closely with other countries to tackle the huge threats that our wildlife and wild places face.'
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