They are one of the most popular sights for nature lovers – and used to be one of the rarest to glimpse.

But now, according to a survey, otters are growing in significant numbers on the Broads and other rivers in Norfolk and Suffolk.

An Environment Agency (EA) survey released yesterday says 56.87pc of selected sites in the East of England showed positive evidence of otters between July 2009 and March.

That figure has risen from only 3.22pc between 1977 and 1979, and 25.82pc between 2000 and 2002.

The increase is being put down to a ban on pesticides, legal protection for the mammals and a significant improvement in water quality.

At a local level, the report shows otter numbers have significantly increased in Broadland rivers, with 48 sites out of 71 showing evidence of the mammals, compared to just three out of 68 sites between 1977 and 1979.

The fifth EA otter survey of its kind says: 'There has been a significant increase in otter range in this area since the last survey.

'The results show that otters are now using most of the watercourses in this area.'

A survey of 45 sites in north west Norfolk showed 23 had some evidence of otters. Between 1984 and 1986 there was no evidence at any of the locations.

The report says: 'There has been a significant increase in otter range in this area since the last survey. Otters now use all the main river but no signs were found on many minor watercourses.'

The EA says numbers show there was also a significant expansion of otter distribution in north Norfolk with the animals using most of the region's larger watercourses.

In the east of Suffolk there were 36 sites out of 60 which had some proof of otters. The last survey between 2000 and 2002 showed there were only 24 locations with some form of evidence.

The survey said: 'There has been a significant overall expansion of otter range in this area and they now use all the main watercourses.' Nationally, otter evidence was found at 58.8pc of sites surveyed in 2009 and 2010. The only down side to yesterday's report was the high number of otters killed on the region's roads.

The report concludes: 'Recovery has been in response to three main factors – the ban on pesticides that caused extinction of otters from many parts in England in the 1960s and early 1970s, legal protection for the otter since 1978 and the significant improvement in water quality in previously fishless rivers since the 1970s.

'The prospects are for full recovery across England probably within the next two decades or so.'