A water company that allowed a sewage treatment plant to pollute drains four times has been referred by magistrates to a higher court for sentencing.
Anglian Water admitted its works at Newmarket serving Cambridgeshire and Suffolk had spilled ammonia.
On one occasion the spillage led to the the deaths of 1,200 fish, Mildenhall Magistrates' Court was told.
The court has sent the case to Ipswich Crown Court for sentencing and Anglian Water said it would fully cooperate.
Magistrates at Mildenhall were told that Anglian Water's pollution offences were caused by operational and management failures.
The first of the offences took place in January 2006 when the level of ammonia discharged was more than twice the maximum allowed.
The Environment Agency's pre-programmed sampling at the sewage treatment works also recorded serious and continuing high levels of ammonia in the two weeks leading up to the breach.
Damage taken seriously
It was also established that the site manager or other employees of the company, had removed, destroyed and falsified information in the site log book which recorded levels of ammonia in the discharge.
An Anglian Water member of staff informed senior management of the situation and the manager was dismissed.
Anglian Water pleaded guilty to three breaches of the Water Resources Act 1991 and asked for a fourth to be taken into consideration.
All the charges related to the Newmarket sewage treatment works.
A spokeswoman for the company said: "Anglian Water is disappointed that this matter has been referred to the crown court but will of course continue to fully co-operate as the legal process continues.
"It would be inappropriate to comment on the specifics of the case, other than to say that Anglian Water has worked closely with the Environment Agency in trying to progress this matter.
"Protecting and enhancing the environment in which it operates is a key priority for Anglian Water, and any event which causes damage or potential damage to the environment is taken extremely seriously."
A date for the hearing at Ipswich Crown Court has yet to be fixed.