Officers from Environment Agency Wales are dealing with an incident in Cenarth, near Newcastle Emlyn, Carmarthenshire, whereby approximately 130,000 gallons of slurry has spilled into the Afon Teifi and a small nearby tributary.
The spill was reported to the Agency on Monday afternoon (10-Dec), when a farmer became aware of a leak in his slurry store.
Officers attended the scene on Monday evening to help stop the leak and were back on site on Tuesday to assess the impact of the spill on the environment.
After inspection of the Afon Teifi, officers reported that the high river flows have quickly dispersed the pollution and little evidence of the slurry pollution remainined.
The small tributary remains slightly discoloured, but officers expect this to clear shortly.
So far there have been no reports of dead fish in either river.
As a precaution, the Dwr Cymru Welsh water drinking water abstraction point at Llechryd was temporarily closed for a short period on Monday night, but has since reopened and there has been no impact on domestic supplies.
A spokesperson from Environment Agency Wales said:
"We're thankful to the farmer for reporting this incident to us, and we will continue to monitor the site over the coming days to check that there are no further impacts on water quality in the rivers.
"We're also advising the farmer on how to conduct a cleanup operation on the farm without causing any more slurry to enter the rivers.
"If anyone notices any further signs of pollution in the area they should report it directly to us through our incident hotline on 0800 80 70 60."