Severn Trent has been hit with a significant fine after a pollution incident in the River Amber resulted in tens of thousands of dead fish.

The company was fined £350,000 at Derby Crown Court, sitting in Nottingham, on 19 April. It was also ordered to pay Environment Agency costs of £68,003, as well as a victim surcharge of £120.

An estimated 30,000 dead fish and 5km of damaged ecology along the River Amber led to proceedings brought against Severn Trent.

On 1 November 2015, the Environment Agency received reports of several hundred dead fish in the River Amber in Derbyshire.

The source of pollution into the river was found to be a release of sodium hydroxide from the Ogston water treatment works, operated by Severn Trent.

Severn Trent identified a leak within a chamber at the treatment works had led to the contents becoming contaminated with sodium hydroxide, which was then washed through the road gully into the River Amber via an outfall pipe.

The Environment Agency said the pollution had a “significant negative impact” on the fish and invertebrate populations within the River Amber. It has been monitoring the natural recovery of the river ecology over the last two years.

“Monitoring has shown that while there have been some improvements, something resembling a full recovery is not expected until the summer of this year,” the Environment Agency said.

In passing sentence, his honour judge Smith, said: “It beggars belief that a company of the size and expertise of Severn Trent Water had no policy whatsoever in respect of potential incidents arising in connection with their dosing chamber, either at this treatment works or indeed at any others throughout the UK.

“To have no policy whatsover when dangerous chemicals could have leaked out in any number of ways is highly negligent. The size and success of Severn Trent makes it even more astonishing.”

A spokesperson for the water company, said: “Severn Trent takes its environmental responsibilities very seriously and we’re disappointed that on this occasion we failed to live up to them.

“We’d like to apologise to the local community, and fully accept the judgement of the court.

“We’re committed to doing everything we can to improve our local environments and we’ve been given a sector leading status by the Environment Agency several times in the last few years.”

They added: “Since the spill at Ogston we’ve strengthened our procedures and have reduced the number of serious pollution incidents by more than half since 2011.  We’ve also donated a further £228,000 to the Derbyshire Wildlife Trust to fund sustainable improvements to the River Amber.”

An Environment Agency officer involved with the investigation, said: “This is a significant fine imposed on Severn Trent Water Limited for causing pollution. I hope it sends a strong message that it is far more cost effective to avoid these incidents, as we will continue to take companies and individuals to task where they ignore their responsibilities.

“Pollution causes damage to the environment and river ecology, in this case sodium hydroxide with a concentration of 20 per cent amounts to a hazardous chemical and the leak affected 5km of the River Amber and killed approximately 30,000 fish and damaged other wildlife.”