A plant nursery has has been fined £10,000 after polluting five miles of a stream in Norfolk.
PS and JE Ward Ltd admitted causing the pollution at Belmont Nursery, Terrington St Clement, in May.
The firm was also ordered to pay £6,178 in costs at King's Lynn Magistrates' Court.
Claire Bentley, prosecuting for the Environment Agency, said that discharge from a pipe into the stream had a "catastrophic impact" on it.
"There was also evidence suggesting that the discharge had been occurring over an extended period," she added.
Miss Bentley told the court that the polluting liquid had come from a stockpile of bulbs and cut flower stems in the yard at the nursery.
Environment Agency officers said they saw black spots in the streem and scum on the surface.
Immediately downstream of the discharge pipe the stream was "entirely full with rotten waste", Miss Bentley added.
The firm's director Peter Ward told Environment Agency officers that the waste had been stored in the yard for two months and the company had not realised there was a problem.
He had not been aware that run-off from "green" waste was highly polluting.
As soon as the company became aware of the problem it blocked the outlet, the court heard.
Deborah Sharples, for the defence, said the company was very sorry for the incident and had taken advice from consultants to ensure it did not happen again.