Teams continue to tackle kerosene pollution on the River Taff
Natural Resources Wales (NRW) is working with partner organisations and the operator in response to the kerosene pollution incident affecting a tributary of the River Taff.
Swift action taken since the pollution was first reported on Friday (16 October) has significantly reduced the amount of fuel reaching the river.
The incident involves complex underground drainage systems and work is ongoing to trace the exact source. This includes specialist techniques, such as drone surveys and use of dyes to support the investigation and assess environmental impacts.
An NRW spokesperson said:
"Our priority remains assisting the operator to find and stop the source of the pollution as quickly as possible while doing everything possible to protect the river and reduce further environmental harm. We are grateful to colleagues and partners for responding rapidly when reports came in, as this has significantly reduced the amount of fuel reaching the river.
"As part of the investigation, we may use a harmless green tracing dye at points during the day to help track water flows and identify the route of the pollution. Members of the public who see the dye should be aware that it is a standard investigative technique and does not pose a risk to people or wildlife."
Wildlife assessments are continuing, and samples collected from the river are being analysed.
While fish have sadly been recovered, the incident had not, as of Sunday evening, been categorised as a major fish kill event. The investigations are also considering any potential longer-term effects on the river's wildlife and ecology.
Public Health Wales had issued the following advice:
"Kerosene vapours may be mildly irritating to the respiratory system and as a liquid to skin. Our current assessment is that people who can smell kerosene may experience temporary irritation, particularly if they are exposed for prolonged periods.
"Public Health Wales advises residents to keep doors and windows closed while the smell is present and to open them again once the odour has passed. Also, as a precaution, to avoid contact with affected water. If in contact, remove affected clothing and wash any exposed skin with soap and water.
"Anyone who feels unwell or is concerned about their symptoms should seek medical advice by contacting NHS 111 Wales.
"Public Health Wales continues to work closely with Natural Resources Wales and other partners to assess the situation and monitor any potential impacts on public health."