Britain's best-known river, the Thames, which flows through central London as well as through historic Windsor and Oxford, is also the country's worst, a new study has found.

Just last month, the UK Environment Agency was celebrating after the Thames was named as the winner of the International Theiss River Prize, beating off the likes of the Yellow River in China and Hattah Lakes in Australia to win the award for the most-outstanding achievement in waterway management and restoration.

"Tighter regulation of polluting industries and our work with farmers, businesses and water companies to reduce pollution and improve water quality, have all helped to make the Thames a living river once again," the Agency's National Conservation Manager, Alistair Driver, said at the time.

However, such jubilation has proven to be short-lived, as Britons themselves have named the Thames as their least favourite out of all of the rivers in England and Wales, thanks largely to its dirtiness and lack of biodiversity.

Responding to the annual study carried out by the Our Rivers campaign – which has the backing of, among others, the WWF, the RSPB, the Angling Trust and the Salmon and Trout Association – members of the public complained that, despite recent improvements, the Thames is still suffering from hundreds of years of lack of investment in sewerage infrastructure, as well as a general lack of urgency when it comes to making the waters cleaner for people and wildlife alike.

In comparison, the Wye, which straddles the England-Wales border has been named as the nation's best river, thanks partly to the fact that its cleanliness and tranquillity make it 'a haven for wildlife' and an ideal place 'to get lost and slow down'.

Such a damning assessment of the Thames by the British public is hardly surprising. According to the Environment Agency's own figures, just 26 per cent of rivers in England and Wales currently meet the cleanliness standards laid out under the European Water Framework Directive.

Moreover, the government department's data also shows that, despite the ongoing improvements of the past three decades, 13 of the 14 sections the iconic river is divided up into are failing to meet the required standards.

Commenting on the most pressing problems facing the Thames, Ralph Underhill, the RSPB's River basin Planning Officer and member of the Our Rivers campaign explained to the Earth Times that, while improvements to water quality levels have been achieved through a focus on direct discharges into the Thames and other rivers, for example through pipes, a broader approach is necessary moving forward.

"Although addressing direct discharges is still important we must also look at the other big sources – nutrient and soils from certain agricultural practices, run off from roads and buildings and physical barriers to fish such as weirs and flood defences," he said.

And, though Britain's current coalition government may be keen on rolling back the state, enhanced cooperation between the government on one hand and private interests such as the agricultural and chemical industries on the other will play a crucial role in cutting down on levels of polluting chemicals and other waste flowing into the nation's waterways.

"We need to see better enforcement of existing regulations, greater uptake of voluntary measures, like the Campaign for the Farmed Environment and more farmers entering land into agreements where they get additional money for protecting and enhancing the environment," Mr Underhill added.

Despite the bleak picture presented by the Our Rivers report, as the recent awarding of the Theiss River Prize served to illustrate, the situation is improving, and the future certainly looks bright for Britain's rivers and the wildlife that lives in them. The coming years will see the completion of the ambitious Thames tunnel, which will go a long way towards addressing the current problem of excess sewerage in the river, while businesses are also becoming increasingly proactive in regulating run-off into freshwater.

But, perhaps above all, the British public are also stepping up their efforts to clean-up the rivers. The fact that the Thames also gained a significant proportion of votes in the 'Best River' category of the study shows is likely to inspire some hope that further water quality improvements are likely, while the numerous local groups working to improve it and its adjoining waterways could potentially play a key role in further boosting standards, particularly if they can get the government on their side.