A portable toilet firm from Walsall has been ordered to pay more than £25,000 after 300 fish were killed by river pollution.

Orchid Investments, which runs D-Tox Waste Management, admitted dumping polluted waste from its chemical toilets into a tributary to the River Avon at Long Marston Airfield, near Stratford-upon-Avon.

The Aldridge-based firm was supplying portable toilets for the Bulldog Bash biker festival when it happened in August 2011.

The ammonia in the toilet waste was toxic to fish and killed several different species including roach, minnows, perch and dace.

At Leamington Magistrates’ Court, the firm pleaded guilty to causing a discharge of chemical toilet effluent without having an environmental permit in place.

The company was fined £16,000, ordered to pay £9,367 in costs and a £15 victim surcharge following an investigation by the Environment Agency.

Usually, sealed plastic holding tanks would have been used to contain the effluent during the event, prior to removal off site to a sewage treatment works.

But on this occasion the company had wrongly assumed the holding vessel was lined and the effluent was discharged directly into the tributary.

A massive operation took place by the Environment Agency to clear the pollution, which covered more than two miles of the watercourse, including the opening of the River Avon.

Officers from the agency also monitored the tributary to minimise the risk of pollution spreading even further down the river.

The court heard the company had expressed remorse and entered an early guilty plea.

Speaking after the hearing, Kate Grimsditch, officer in charge for the Environment Agency, said: “Rivers and watercourses are an important part of our environment, and we must do our best to protect them from pollution.’’