An abattoir in Wigton has been fined £5,000 after a leak at the facility allowed effluent containing blood to contaminate the nearby Pow Beck tributary.
The company in question was also ordered to pay costs of £3,127 at Carlisle Magistrates Court.
According to the Environment Agency, the leak turned the waters "blood red" and caused significant damage to the eco system of the beck.
The pollution led to fungus growth across a large area, causing oxygen levels to fall, resulting in death and damage to water life.
Environment Officer Chris Boak said companies need to be aware of their duties and ensure that pollution is not caused by their actions.
"This was a serious organic pollution incident which damaged the eco system of the watercourse and caused distress to the public due to the change in the colour of the water," he added.
Meanwhile, the Environment Agency this week announced plans to clamp down on illegal anglers across the country.
Written by Fiona Mayers