A spokesperson for the water company said: “Following our initial investigation we believe that the contaminant originated from highways surface water run-off entering the watercourse, and are in the process of preparing our detailed report to submit to the Environment Agency.
“However, our investigations suggest that this is not a Yorkshire Water-related incident.”
An EA spokesperson said there was “no obvious impact on the wildlife”.
Chalk streams – which come from underground chalk reservoirs – are considered to be rare and special water sources.
Residents were thanked for reporting the pollution to the EA.
Anyone with further information about the source of the contamination is asked to contact the agency.