A large amount of slurry has polluted a tributary of the River Taf in Carmarthenshire.
Environment Agency Wales were called to the Nant Cwmfelinboeth, north of Whitland, late last night after a call from member of the public.
Biologists and fisheries officers are currently assessing the full impace on the environment and local wildlife.
– An Environment Agency Wales spokesperson
A significant quantity of slurry has entered the river and we are continuing work to find its source and to establish what impact it may have had.
Local people should be aware that the river is likely to remain discoloured for several days and they may also notice signs of a foam like material in the water as the slurry begins to break down.
This is one of a number of incidents that has happened in the area in recent times and once we have located the source we will take the appropriate action against whoever is responsible.
Any one who spots any further signs of pollution in the river should report it via the agency's incident hotline on 0800 807060.