ENVIRONMENT Agency officers were called to a Clayton West stream after slurry got into it, a court heard.
The man held responsible was fined £5,000 by Huddersfield magistrates.
They heard that 700 yards of Duke Wood Dike was affected after farmer Stephen Brook spread slurry on nearby fields.
Brook, of Wheatley Hill Lane, Clayton West, admitted polluting the stream on or before January 24.
A member of the public called the Environment Agency after the incident, the court was told.
Brook was also ordered to pay £2,617 to the Environment Agency, which brought the prosecution.
Environment officer Dave Preston said after the hearing: "This case highlights the need for all farmers to take extra care when spreading slurry to ensure that it does not run off into a watercourse."