Anglian Water has admitted responsibility for polluting the Stour Brook with sewage on Tuesday (August 5).
The pollution from the incident has already killed thosands of fish, with warnings being given to dog walkers and anglers in the area to stay away from the water.
Antony Innes, from Anglian Water, said: “We deeply regret that a problem with equipment at our Haverhill water recycling centre led to sewage entering the brook.
“Our alarm systems alerted us to the problem immediately, and we dispatched engineers to the site to investigate the problem. Tankers have also been stationed at the site to help manage the situation. Repair work is already underway.
“We are working closely with the Environment Agency to assess the situation, and to protect and restore the brook. This includes using aerators which increase oxygen levels in the water, to support wildlife.
“We take our environmental responsibilities incredibly seriously. We are doing everything we can to remedy this situation, and will continue to monitor the situation over the coming days so we can intervene immediately if we have to.”
Councillor Tony Brown said: “It’s shocking. Year on year, it’s been thriving with fish down there, it’s been an asset to Haverhill.
“When I went down there, there was nothing left. Everything’s dead. There are no fish at all where, once, there were whole schools of fish.”
The Environment Agency is currently investigating the incident.