An investigation was launched after a stream turned a vivid shade of green. The changes happened to the tributary of the River Clywedog in Johnstown, Wrexham.
Natural Resources Wales launched an investigation after being alerted to the pollution.
The source of the unusual colour was traced back to a business on a nearby industrial estate earlier this week.
Officers from the environmental organisation say that the discharge source has now been stopped.
The agency said it was continuing to work with the site.
A statement from NRW said: "We were able to trace the source back quickly to a business on a nearby industrial estate who have now stopped the discharge. We will continue to work with the site to ensure environmental compliance"
You can report signs of pollutions to the incident hotline 24/7 on 03000 65 3000.
Read next:
