An agricultural college in Sussex has been fined £50,000 for polluting a stream, causing the deaths of more than 1,500 fish, according to the Environment Agency.

Plumpton College spread water containing a high amount of cow slurry as fertiliser on a field it managed, which ran off into ditches and land drains before flowing into a nearby stream.

The waterway was visibly brown on top and smelt strongly, the Environment Agency said, and the contamination in November 2016 caused the deaths of protected species of fish, including migratory trout.

It was classified as a category one incident by the Environment Agency, its most serious level.

A court heard that the volume of liquid spread was more than the field could absorb and, as the ground was also frozen, much of the contaminated water flowed into Plumpton Mill Stream.

A member of the public reported the incident to the Environment Agency, which said the college did not report the pollution or have an emergency plan in place for dealing with slurry spillage.

The college admitted the incident was the result of a mistake by a staff member, who accepted a formal caution, and conceded that the weather conditions and field were not suitable for spreading the slurry.

The college, in Ditchling Road, Lewes, pleaded guilty to the offence at Lewes Crown Court last year, according to the Environment Agency.

It said the college was fined £50,000 at Hove Crown Court on Friday and ordered to pay £44,852 in costs.

Ed Schmidt, environment management team leader in Sussex for the Environment Agency, said: “Poor management, a lack of contingency planning and inadequate infrastructure at the farm resulted in a totally avoidable pollution incident that had a disastrous effect on the local environment.

“It is even more disappointing that a college that specialises in agricultural practices and teaches farmers of the future failed to take all reasonable actions, and was wholly negligent in preventing this incident from occurring in the first place.”

A statement by Plumpton College said: “The college took some solace today from the Judge’s finding which supported our own internal investigation that this was attributable to an inexplicable course of behaviour by an ex-member of staff who left the college in 2017, and that had this individual not acted in this way, no pollution event would have occurred.

“Judge Barnes supported the college’s view that the incident was not indicative in any way of the College’s current performance and standards and indeed praised the significant progress made over recent years.

“The college is looking forward to receiving record numbers of land based students for the start of the new academic year, as it continues to achieve some of the highest pass rates amongst its peers nationally.

“Its new cohort of agriculture students will learn on the farm which is today accredited by Red Tractor and the prestigious Leaf Marque for its environmentally friendly farming practices.”