Members of the public are being told not to worry if they spot red dye in the River Calder this week.
The dye is being added to the river in Mirfield today as part of a detailed water quality study being carried out by Yorkshire Water.
The work is being regulated by the Environment Agency, which will ensure that the minimum amount of dye is used so that there is no environmental damage as a result.
The dye will be added to the River Calder at Hopton New Road Bridge in Mirfield, at noon.
Chris Barker of the Environ-ment Agency said: "The dye will not cause any harm to the wildlife in and around the river and should only be visible in the river for a short distance below the bridge."
The study is being carried out by Yorkshire Water to assess the required improvements to the sewerage system in the Calder Valley. Using the dye will give the company valuable information about river flows in the Calder.
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