Dying eels were spotted near Swalecliffe Brook – after untreated sewage was discharged from a nearby pumping station as Whitstable prepared for its annual oyster festival.

The incident on July 21 last year was reported by a passer-by who spotted the brook “black and smelling of sewage” near to the sea.

A local festival supplier was forced to obtain oysters from other areas after fears over contamination of oysters.

Now Southern Water Services has admitted breaching regulations because of an undue delay” in tackling the problem, causing “the prolonging of the incident”.

Prosecutor Richard Banwell told Canterbury Crown Court how Environment Agency Officer James Pym was called to the pumping station and discovered only one of three pumps working.

“On inspecting the watercourse, it was apparent that a discharge of sewage had occurred.

“The water was discoloured and had a distinct sewage odour. Dead sticklebacks and eels could be seen. Test results of the water confirmed the brook had been subject to significant organic pollution.”

The court heard that a brown trout, 93 sticklebacks, a goldfish and 155 eels, which are critically endangered species, had died.

After the alert, Canterbury City Council immediately put up warning signs alerting the public to the problem along one of Kent’s moist popular beaches.

Mr Banwell said the area is popular for the harvesting of oysters and tests later showed there were “higher levels of E coli than would have been expected at that time of year.”

Judge Adele Williams heard that Seasalter Shellfish had stopped harvesting the day after the incident and the owners of West Whelks, one of only two suppliers to the annual oyster festival, said it would not take any of the oysters to the festival “due to the risk of contamination.”

Mr Banwell added: “Last year would have been the first time in a few years that the festival would have been supplied by a majority of local oysters rather than those harvested outside Whitstable.

“In the end, West Whelks obtained oysters from elsewhere and sold 35,000 of them during the festival week.”

The case was adjourned until November when Southern Water will continues its defence and the judge will decide what level of fine to hand out.