It may not seem the obvious place to set up home and forage for food – but a family of otters has been caught on camera near sewage works in Dereham.

The night-time images of the elusive animals were taken on camera traps set up to monitor wildlife activity at the treatment plant at Rushmeadow.

The equipment was installed by Anglian Water (AW), which also recently launched region-wide survey into otter populations and habitats.

Mike Drew, the company's biodiversity officer, said: 'We know many of our sites are good for wildlife, because of where they are, their size and the fact they are largely undisturbed.

'So we were hoping for something a bit special and otters certainly fit the bill. To get such lovely pictures of these beautiful and elusive creatures is very exciting.'

AW funds a network of almost 50 voluntary RiverCare groups, including those in Norwich, Great Yarmouth, Fakenham and Sheringham. Each is given support to adopt and look after a local stretch of river.

Run by the charity Keep Britain Tidy, the RiverCare scheme has created an army of volunteers to help record where otters can be found in its region.

The Otterly Fabulous Survey is being run through RiverCare's new Facebook webpage, allowing volunteers – and anyone else who wants to take part – to post their findings online.

All the information gathered will be shared with the region's wildlife trusts and used to guide future conservation efforts.

Mr Drew said: 'We bought two of these camera traps as a trial to see what they might be able to tell us about the wildlife at our sites.

'Knowing what's there is the first step towards making sure we do what we can to protect and encourage some of the countries rarest plants and animals. It's also great to be able to share such fantastic pictures.'

Otters suffered huge declines in the 1950s and 1960s due to pollution, habitat loss and poisoning due to the widespread use of organochlorine pesticides.

?More information about the otter survey can be found at www.facebook.com/RiverCare and www.rivercare.org.uk.