Natural Resources Wales (NRW) have confirmed that around 500 fish have been found dead at Nant Cylla in Penpedairheol – Nearly five times more than first thought.
NRW, who were at the site on Saturday, May 25, initially believed that around 100 fish had died, but have now confirmed that the number is in fact much higher.
The organisation launched an investigation to establish the cause of death after being called to the scene on Saturday, May 25.
The investigation, which was carried out on Sunday, May 26 and Monday, May 27, confirmed that the trout all died along a one-kilometre stretch of water.
Water samples and dead fish have been taken to a laboratory to be analysed.
David Letellier, Operations Manager from NRW, said: “Protecting Wales’ fantastic rivers is incredibly important for us. As soon as we had reports on this incident our officers were on site to investigate.
“Unfortunately, final numbers of fish killed by this pollution is much higher than we initially thought and has had a devastating effect on local fish stocks.
“We believe we have found the source and we’ll consider what action to take next, including appropriate enforcement action against those responsible.”
Mr Letellier added: “We are incredibly grateful to those who reported this incident to us and encourage anyone to report signs of pollution to us on 03000 65 3000 so we can respond.”