Thames Water has been ordered to pay more than £700,000 for polluting the Maidenhead Ditch – killing fish and leaving many in distress.

The case was brought by the Environment Agency (EA) after Thames Water caused pollution from its site at Maidenhead Sewage Treatment works (STW) to enter the Maidenhead Ditch – which joins the River Cut – a tributary of the Thames which is home to Bray Marina, South East Water’s public water supply waterworks as well as a well-used amenity for paddle borders and other water users.

An officer said the EA believes up to around 30 million litres of sewage polluted the ditch, causing the deaths of hundreds of fish.

The court heard how in June 2014, the firm caused pollution of the watercourse with raw sewage. Maidenhead STW has a permit to discharge storm sewage in storm conditions into the watercourse.

The permit aims to deal with the high flows which can result during periods of extreme rainfall.

In June 2014 there were no extreme weather conditions, the EA said.

Maidenhead STW also has another permit to discharge treated final sewage into the watercourse as it includes human waste, a variety of pollutants, organic materials and chemicals.

But the Environment Agency told the court how Thames Water did not meet the conditions of these permits around the time of the incident.

The court heard how sewage and partially treated sewage respectively ended up in the watercourse as a result of poorly performing equipment.

Environment Agency officers rushed to the site as soon as a member of the public alerted the incident hotline after witnessing a grey and odorous cloud of polluted water entering the Maidenhead Ditch and River Cut from the STW.

Officers carried out monitoring for water quality and took water samples of the watercourse at various locations.

The results revealed very low dissolved oxygen levels – indicating that oxygen was stripped from the water as a consequence of pollution last month.

Investigations carried out by Environment Agency officers revealed further failures by TWUL management.

This involved repeated discharges of untreated or poorly treated raw sewage into the river and failing to react adequately to alarms used to alert them to the serious problems.

Log book entries suggest ongoing discharges and other problems at a site that was struggling to cope.

Environment Agency officer Ben Govan said: “Our officers believe up to around 30 million litres of sewage polluted the ditch.

“Hundreds of fish died and the environment suffered as a result of Thames Water’s failures.

“Pollution could and should have been avoided had the many warnings and alerts leading up to the incident been acknowledged and dealt with properly.

“We take these types of incidents very seriously and will do everything within our powers to safeguard the environment and people affected, and that includes holding those who put the environment at risk to account for their actions”.

On Wednesday this week, Thames Water was ordered to pay a fine of £607,000, costs of £100,000 and a victim surcharge of £120 at Aylesbury Crown Court.