The Environment Agency said that a "serious pollution" incident that turned a small stream bright blue has had a "severe environmental impact," and the public should avoid contact with the brook.
The pollution incident at Littleham Brook in Exmouth caused the water to turn bright blue, and a bathing advisory was issued.
The pollution incident was reported on Friday, September 11, but the effects of the "industrial source" incident continue to be felt a week later.
The Environment Agency (EA) posted an update yesterday as it continues its work to identify the pollutant and determine how much entered the brook.
It has been classed as a 'Category 1' incident, the most serious pollution category, as EA said it reflects the "severe environmental impact and the significant time the brook will need to recover".
EA advised that the public should avoid bathing at Exmouth and avoid contact with the brook.
The agency said it is meeting with East Devon District Council, the UK Health Security Agency and the Animal and Plant Health Agency regarding the incident.
The Facebook post from EA said: "Our investigation continues, including work to identify exactly what the pollutant is and how much has entered the brook. We suspect it is from an industrial source.
"How serious is this? We've classed this as a 'Category 1' incident, the most serious pollution category. This reflects the severe environmental impact and the significant time the brook will need to recover.
"We're meeting this afternoon [yesterday] with East Devon District Council, the UK Health Security Agency and the Animal and Plant Health Agency.
"Together we'll review our advice against bathing at Exmouth and update public health guidance relating to the brook.
"Please continue to avoid bathing at Exmouth and avoid contact with Littleham Brook until we advise otherwise."
Serious Pollution in Devon Brook Draws Public Warning