River Dulais milk spill 'seven times more polluting than slurry'
Milk is seven times more polluting than cattle slurry when it enters the river, according to Natural Resources Wales (NRW).
But Ioan Williams, of NRW, said there were no signs of damage to fish stocks after 28,000 litres of milk spilled into the River Dulais after a tanker crashed on Wednesday.
Mr Williams said milk "takes oxygen out of the water", but added it was "reassuring" no dead or distressed fish had yet been found.
The river, which is a tributary of the River Tywi, is now running clear but a milk "slug" is reported to be travelling slowly downstream.