Legal action seeking compensation of people affected by local river pollution is to be extended to cover Welsh Water.

Hundreds of people who claim to have been affected by river pollution in Mid Wales and Herefordshire are threatening to expand their legal action.

Those living near the Wye, Lugg and Usk say they have been robbed of the rivers they enjoyed playing in as children due to the smell and sludge caused by pollution.

They have previously launched a legal case against the firms involved in large-scale chicken farming locally - but now plan to extend this to cover Welsh Water as well, in the biggest claim of its kind in the UK.

Welsh Water said it was investing £2.5bn over the next five years to improve the environment.

Lawyers representing the group have written to the water provider, claiming sewage spills have interfered with the public's enjoyment of the rivers and negatively impacted on local businesses.

The three rivers are protected for their importance to rare wildlife - including otters, freshwater pearl mussels and the Atlantic salmon.

But, in recent years, the Wye in particular has become the focus of widespread concerns over the worsening state of the UK's waterways.

The river flows for 155 miles from its source in the Cambrian mountains along the border between Wales and England to the Severn estuary.

Law firm Leigh Day said it was acting on behalf of more than 2,000 individuals and businesses, bringing a class action lawsuit which would seek compensation for local people.

While it acknowledged the bulk of the pollution was due to "industrial-scale chicken production" it alleged sewage discharges "high in phosphorus and bacteria due to human faeces" were another contributing factor as they resulted in "odour, insect swarms, biodiversity loss and poor water quality".

Welsh Water has been sent a letter from the firm setting out the details of the claim, and has until March 17 to respond.

"At present this will be the biggest nuisance claim for sewage operations against a water company in the UK," said Oliver Holland, partner at Leigh Day.

"But with communities up and down the country impacted by sewage pollution in their waterways this case has the possibility to set an important precedent."

Charles Watson, chair of campaign group River Action, said the addition of Welsh Water as a defendant meant the legal action was "clearly shaping up to be one of the most significant pieces of litigation relating to river pollution yet witnessed in the UK".

Welsh Water confirmed it had received the letter and would "require time to consider the contents carefully before responding".

"We take our responsibility for protecting the environment seriously and over the next five years will invest £2.5 billion to improve the environment," it said.

Avara Foods, one of the UK's biggest food producers, as well as its subsidiary Freemans of Newent and its 50% shareholder Cargill plc are also named as defendants in the proposed legal action.

Avara Foods previously said: "We consider the allegations made by Leigh Day to be factually incorrect and fundamentally misconceived.

"We are proud of our business, providing high-quality and affordable chicken and turkey for consumers, and we will vigorously defend our position."