The incident came to light on 1 April last year when a member of the public saw dead fish on the Werrington Brook, Werrington.
Environment Agency officers sent to the scene found that the brook contained high levels of anionic detergent, the main constituent of shampoo. Levels were as high as 329 milligrams per litre - way above the 0.5-80mg/l needed to kill fish.
Further investigations traced the pollution to the car park of toiletries manufacturer Potter & Moore Innovations. Brown liquid was leaking out of containers in the car park and running into a surface water drain. A sample taken from the drain contained 92,800mg/l of anionic detergent.
The site's manager said waste shampoos, foam baths and shower gels had been stored in the containers following a restructuring of the business.
He assumed they were safe for storage and said vandals must have damaged them, causing the leaks.
Over 200 litres of product was lost in the incident, which polluted around three kilometres of the stream for over a week.
Appearing before Peterborough magistrates on 20 January, the company pleaded guilty to causing polluting matter to enter controlled waters, contrary to section 85(1) of the Water Resources Act 1991. It was fined £6,000 with £4,542 costs.