"The court noted that PGG Wrightson and Carrfields are large companies who had been very careless about how they managed disposal of animal effluent," said Dr Peet.
"The judge commented that commercial operators should be aware of their legal responsibilities and manage their business accordingly.
"In particular, he noted significant amenity, environmental, and cultural impacts.
"We recognise that the companies' guilty pleas were a useful acknowledgement of the offending which reduced the time and cost of prosecution."
Dr Peet said Horizons has an active compliance monitoring programme and also responds to pollution incidents.
"Another significant prosecution was adjourned today, and four further formal investigations are under way.
"Members of our community are encouraged to report any environmental incidents to our 24 hour Pollution Hotline on 0508 800 800."