Volunteers have been helping the City Council clear rubbish from the River Soar
The return of otters to the River Soar through Leicester has been attributed to an improvement in water quality.
The Environment Agency reports rivers in England and Wales have been clearer year on year for the past two decades.
Adrian Lane, a Senior Riverside Officer for Leicester City Council, said the return of the otters after over 30 years was a positive indication.
He cites poisoning from agricultural chemicals as a major factor in the the mammals' previous decline.
Toxins are taken up by the insects, small fish, eels and crayfish that are eaten by the otters, eventually leading to their death.
Adrian also reported an increase in the number of grass snakes, who feed on frogs and newts along the waterways, and kingfishers, who he hopes will return to establish breeding territories as the freezing weather clears.
The City Council have been working with local volunteers to help
clear floating rubbish from the waterways
, sharing the responsibility of providing a healthy environment for nature to thrive.
A clean-up of the Leicester stretch in 2009 saw the extraction of 20 traffic cones, six bicycles, one bus stop, several pallets, and four shipping trolleys.
The authority have also been involved in a project to clear the invasive weed, floating pennywort, from the River Soar.
However Adrian was keen to stress maintaining stable biodiversity it is as much about prevention as cure.
"I've been doing my job for over 20 years now and it's partly a failing on us.
"We've failed in getting that message over to people about what to do with their litter and people still throw it around, they're careless with it and this is the problem," said Adrian.
"At the end of the day there's three fundamentals; we want clear air to breathe, we need good land to grow food and we need water.
"If we can't look after those resources the human race will suffer. And we've got to sent that example in Leicester," he added.