Sub Micron Industries has been fined £4,500 ($6,904) by Huddersfield Magistrates Court for polluting the River Colne and killing hundreds of fish.
During the Environment Agency's investigation the factory was found to have released pesticides and other chemicals into the water of the River Colne.
Levels of the highly toxic chemical permethrin were found to be 13 million times higher than the allowed level and deltamethrin was also discovered at 4 million times the allowed level, officers said.
Slaithwaite-based Sub Micron will pay the £4,500 ($6,904) fine plus £3,580.83 ($5,488) in costs and the £15 ($23) victim surcharge at £2,023.96 ($3,100) a month starting in April, according to examiner.co.uk.
