A farm has been ordered to pay a fine of £34,000 after a spillage of agricultural chemicals led to 15,000 fish being killed in waterways in north Essex, a court has heard.

Representatives of Berwick Hall Farm appeared at Chelmsford Magistrates Court to answer charges that thousands of litres of poisonous liquid had been allowed to flow into a river at Toppesfield, near Halstead. after a crop sprayer overturned last year. The farm was fined £34,000 and ordered to pay full costs of £32,997 and a victim surcharge of £120.

Magistrates heard that Matthew Clark, the company director, was driving a tractor over a badly constructed bridge trailing a sprayer of agricultural chemicals when it tipped and emptied much of its contents into Toppesfield Brook, a tributary of the River Colne.

Anne-Lise McDonald, prosecuting for the Environment Agency (EA), said the incident could have been prevented had the bridge been constructed and maintained properly or if the director had chosen a different route to avoid the river crossing.

The court heard that around 12,300 fish were killed in the River Colne and 3,000 were killed in the brook during the pollution on June 13 2012.

Agency fisheries officers mounted a round-the-clock rescue of almost 8,000 fish after a major incident alert was broadcast.

Solicitor for the defence, Stephanie Coates, said in mitigation that the company had acted swiftly to report the incident and had shown remorse for the damage caused.

After the hearing EA officer, Peter Cooke, said: “This incident had a catastrophic impact on fish and aquatic life and affected drinking water supplies many miles away. The huge costs incurred should act as a sobering reminder to all pesticide users of the acute and toxic nature of the chemicals they use.”