Appearing before Worcester magistrates on 21 June, animal feed manufacturer ABNA pleaded guilty to causing polluting matter to enter controlled waters, contrary to section 85(1) of the Water Resources Act 1991.
The court heard how the Environment Agency was called to Battlefield brook near Bromsgrove on 7 September last year. Officers found the brook was full of effluent and that much of its freshwater shrimp population had been devastated.
Samples taken from the brook later revealed that it had a biochemical oxygen demand over 30 times stronger than raw sewage.
The spill was traced to ABNA's site nearby, where it makes pig feed from surplus food, including chocolate.
Further investigations revealed a pump in the company's effluent pit had failed, causing effluent to overflow through a hidden pipe into the brook.
In mitigation, the company said the incident was "an isolated lapse" and drew attention to its previously good record. A drainage survey of the site in 1999 had failed to spot the discharge pipe.
ABNA was fined £10,000 and ordered to pay costs of £3,188.