River Action, an anti-pollution charity, is seeking a judicial review against the Environment Agency (EA).

The charity claims it is allowing destructive levels of nutrients from organic manure to enter the river.

Around 20 million chickens are estimated to be raised in the Wye catchment which makes up about 25% of the UK's poultry population.

A large amount of organic manure has been spread over the area, with a substantial increase in phosphorus levels in the soil.

The 130-mile-long river crosses over the border between Wales and England.

When rainwater washes the phosphorus into the river, it can cause prolonged algal blooms which turn the colour of the water to an opaque green.

The High Court in Cardiff heard statutory guidance from the Department for Environment, Food and Rural Affairs states land managers should avoid spreading manure during a crop rotation that raises phosphorus in soil above a certain level.

That is unless it is not reasonably practicable to do so, or all appropriate precautions have been taken to prevent any diffuse agricultural pollution.

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Lawyers representing River Action said there was "no dispute" the River Wye was in "very poor condition".

"This is in large part due to unacceptably high levels of phosphate in the water," the court heard.

"We are concerned with the large-scale shovelling of manure from large sheds full of chickens onto the land."

Lawyers for the EA rejected claims it had not taken action and said warning letters had been sent out to those who may have been in breach of the regulations to "bring them in line" with the rules.

After considering all submissions, Mr Justice Lane granted permission for a full judicial review.