River Dulas pollution: Thousands of fish dead
More than 2,000 fish have died after a river was polluted with slurry, Natural Resources Wales (NRW) said.
About three miles of the River Dulas, near Capel Isaac in Carmarthenshire, has been affected since the pollution was reported on 8 July, NRW added.
Its officers are at the river, a tributary of the River Towy, taking samples and conducting fish surveys.
Invertebrates and fish, including brown trout, bullhead, eels, lamprey, stone loach, minnow and salmon, are affected.
"Unfortunately, we can confirm that the total number of fish that were killed is significant and will have an adverse effect on the river for years to come," Ioan Williams from NRW said.
"Our staff have been working tirelessly to gather evidence about this incident and we will use that evidence to consider future legal action."
Mr Williams said it was "completely unacceptable and irresponsible that a small number of farmers are not taking notice of good practice and regulations".
It comes at a time when salmon and sewin stocks are at a "very low level", Mr Williams added.