CONTAMINATED water used to battle a blaze at the UK's largest wood recycling centre turned a river brown and killed fish.
High levels of ammonia polluted the River Don, and a tributary known as Sledbrook Dyke, after water put on a wood chippings fire at the Plevin factory in Crow Edge entered the waterway.
Water quality samples have been taken from the river and the dyke, where at least 20 dead brown trout have been found.
The Environment Agency is investigating the cause of the fire, which was still burning ten days after it started, and how the recycling facility is being managed to ascertain whether any rules have been breached.
An Environment Agency spokesman said: "Should any offences be found, we will consider the most appropriate course of action in line with our published procedures.
"We have issued an enforcement notice to Plevin which prevents the firm from receiving any further waste materials onto the site. The notice also requires the firm to prevent fire water run-off from entering watercourses."
Millions of litres of water have been used to tackle the fire since firefighters received a call at 8.10am on Monday June 2.
A Plevin spokesman said: "Health and safety is of paramount importance to us and we be will readdressing our operating procedures to minimise the risk of this happening again. We sincerely apologise to residents that have been affected during this time and will be in touch with those that have raised issues on an individual basis.