In what lawyers are billing as the UK's biggest environmental pollution claim, over 1,300 people have signed up to sue Avara Foods, its subsidiary Freemans of Newent, and Welsh Water for turning the River Wye and River Usw into summer-themed science experiments. The rivers allegedly turn green, smell, and get slimy - which is great if you're a pond scum enthusiast, less so if you're a fish.

Avara Foods, one of the country's biggest industrial chicken producers, is having none of it. At a preliminary High Court hearing in London on Monday, Charles Gibson KC, representing Avara and Freemans, called the pollution claim "entirely inferential and an oversimplification." In written submissions, he argued the claim is "fundamentally misconceived in law and in fact, lacking in any proper scientific basis, and misunderstands how poultry farms in fact operate."

About 24 million chickens - roughly a quarter of the UK's entire chicken population - live in the Wye's catchment area, mostly in huge battery farms. The claim alleges that pollution comes from water runoff containing high concentrations of phosphorus, nitrogen, and bacteria from spreading thousands of tonnes of poultry manure and sewage biosolids. High phosphorus and nitrogen levels cause algae blooms that cut oxygen, suffocate fish, and create lovely smells as everything decays.

Anneliese Day KC, representing the claimants, argued that the rivers' ecological decline has harmed the claimants, who seek substantial damages and injunctive relief. She noted that 1,309 people have joined so far, and about 300,000 people live in the Wye and Usk catchments, depending on them as a "shared environmental resource."

Judge Cook described the claim as an "omnibus" on which "anybody can get on board," adding he was "quite frankly taken aback by how the claimants have gone about this." The hearing wrapped up Monday, with a further hearing expected later. In the meantime, the rivers remain green, slimy, and presumably unimpressed with the legal arguments.