West Coast Regional Council hopes a hefty "dirty dairying" fine for a Westland farming company serves as a warning to persistent polluters in the dairy industry.

Potae and van der Poel Limited was fined $120,000 in the Environment Court this week for illegal dairy effluent discharges on three of its seven farms at Whataroa in what the Council claims is the worst offending its ever seen.

The regional council found overflowing effluent from ponds and irrigators on each of the three farms on at least 45 occasions in 2008.

Consents and compliance manager Colin Dall says the fine should serve as a deterrent to farmers who break the rules. He says two more West Coast effluent discharge prosecutions are pending.