Severn Trent Water could be hauled before the courts over the deaths of thousands of fish killed by a toxic substance in Black Country canals.

Anglers who are still pulling out hundreds of dead fish from an eight-mile stretch of Wolverhampton’s waterways said that a dossier was being compiled by Fish Legal, which fights against water pollution across the country.

Around 2,000 dead fish have been discovered since a toxic substance from the Severn Trent sewage plant near Autherley Junction, at Oxley in Wolverhampton, ran into the waters more than a week ago.

The Environment Agency said the pollution had spread as far north as Wheaton Aston and as far south as Dunstall Park.

Today it emerged a dossier into the events of the past week was being compiled.

It could lead to legal action against Severn Trent, which has confirmed the source of the problem was its Barnhurst sewage plant where ammonia is reported to have been discharged into the canal network after leaking into the treatment works.

Alan Gough, of Wolverhampton Angling Association, said: “There are so many fish still being found. There’s a lot of heron in the canals so we want people to report it if they see any birds have been affected by this.

“At the moment we are getting all of the information together for Fish Legal such as how the canal was before and what it is like now. This will go to court.”