yorkshire Water has been hit with a £5,000 fine after pollution from the works at Copley got into the River Calder.
The firm admitted it had exceeded the amount of biochemical oxygen demand, which reduces the amount of oxygen in the river, in April last year.
A reading by the environment agency confirms 73.6 milligrams per litre of biochemical oxygen demand were in the water. The amount permitted is 70 milligrams.
Just 20 days earlier, the level recorded was 136 milligrams per litre.
Yorkshire Water was given a formal warning by the Environment Agency on that occasion, but was prosecuted for the second reading of 73.6 milligrams three weeks later.
Paul Harley, for the environment agency, told Calderdale magistrates that a malfunction in one of the two centrifuges at the Copley site, coupled with bad weather the previous winter, had put a strain on the system.
“Yorkshire Water took a risk in the way they dealt with the situation,” he said.
Perminder Kaur, for Yorkshire Water, told magistrates: “This was not a case where there was a deliberate breach of the law of actions motivated by cost savings – far from it.
“Yorkshire Water also reported the increase in biochemical oxygen demand to the environment agency themselves and pleaded guilty at the first opportunity.
“No fish or other wildlife were killed because of the pollution,” she added.
As well as the £5,000 fine, Yorkshire Water must pay costs of £1,593 and a victim surcharge of £15.