The company pleaded guilty to the incident, which saw the River Fal polluted with slurry in July 2003.

The incident, which was reported by staff at the company to the Environment Agency, discoloured a stretch of the river from St Stephen to Grampound.

The Environment Agency said it would continue to work with Imerys to improve its pollution record.

During the incident, a pipeline in the Melbur area carrying china clay slurry failed, spilling the clay residue into a tributary of the Fal.

Environment Agency staff found the river was a rich white colour at Terras Bridge.

Agency investigating officer Steve Clark found that the discharge had come from a section of pipeline that had been repaired only a few months earlier.

Mr Clark said the agency would continue to work with the china clay company to help it to improve.