FISH were killed as a long stretch of the River Colne was polluted.
Experts from the Environment Agency are trying to trace the source of the pollution, which carpeted the river in white foam.
The foam stretched for 3.5km through Aspley yesterday and killed at least 100 fish.
Eye witness Mr Graham Wilkinson, of Trinity Street, Huddersfield, said: "It looked as though there was a covering of snow on the river.
"It is a shame as the river has been cleaned up in recent years and there are now fish such as trout and grayling in there."
An Environment Agency spokesman said: "The incident was reported to us at 1pm yesterday and we had officers on site trying to trace the source of the pollution.
"The foam was being blown off on to nearby properties but we believe it is only detergent.
"Inquiries are continuing to trace the source of the pollution, which killed at least 100 fish."
