A mystery oil slick has been spotted in the River Wansbeck.
Concerned residents noticed the oily sheen near Elliot Bridge in New Market, Morpeth, last Thursday morning, spreading to Sheepwash.
Morpeth town councillor David Clark reported it to the Environment Agency, but when an inspector arrived it could no longer be seen.
The officer spoke to fairground operators who were setting up in the area to advise on diesel storage, but there is no suggestion they were responsible as the oil had been further upstream and on the opposite bank.
An Environment Agency spokesman said: “An officer went down to the site, but when he got there, there was no sign of pollution. It was raining heavily at the time, which would have washed it through.
“We do appreciate it when people bring these things to our attention. If they see anything like this they should report it to us as soon as they can. The faster we know about it, the quicker we can respond.”
The 24-hour free hotline number is 0800 807060.