Scottish Water has launched an investigation into the potential dumping of chemical waste by tankers in Aberdeenshire.
"Unexplained" influxes of chemicals has sparked an appeal for communities in the Donside area to be alert to any unauthorised use of the public sewer network.
Scottish Water said the influxes had happened on several occasions, particularly at the Waste Water Treatment Works that serve Kemnay, Oldmeldrum and Daviot.
The water company is seeking information about any "unusual activity" by tankers in the area which could be linked to the problems being experienced. Scottish Water added it was not aware of any impact on people or livestock.
The issue has led to its staff facing what the company described as a "race against time" to stabilise the water treatment process to prevent damage to the local environment.
Scottish Water said it was in touch with large commercial customers in the area to ensure there were no problems with the waste they were licensed to discharge.
Regional waste water operations manager Craig Low said: "Each of our Waste Water Treatment Works across Scotland is designed to meet the needs of homes and businesses within its area, while protecting the local environment.
"Any sudden and significant change in the strength and composition of waste water has potential to disrupt the treatment process and harm the natural environment that it works to protect.
“Following several events which our teams have had to respond to in Kemnay, Oldmeldrum and Daviot, we are investigating all potential causes."