The smoke from the fire could be seen by drivers on the M69
Tests are being carried out on river water close to the scene of a factory fire in Warwickshire after anglers reported fish were dying.
Fire crews were called to Abbey Metal Finishing in Weddington Road, Nuneaton, where a two-storey building was on fire.
Drivers on the M69 in Leicestershire reported seeing a large plume of black smoke.
The water run off from the fire could have got into the nearby River Anker.
The cause of the fire is not yet known and residents were told to stay inside and keep windows and doors shut due to possible impact of chemicals involved.
Two nearby schools remain open and an exclusion zone around the scene has been set up, Warwickshire Fire and Rescue Service said.
Although the bulk of the fire is now out, firefighters will remain on site until the area is safe, the spokesman added.
The firm deals with finishing processes associated with aerospace, defence and engineering industries.
Weddington Road was closed and 16 fire appliances were at the scene at the height of the fire.
It is thought about 70 people work at the unit but it not known whether anyone was in the the building at the time.
Alan Franks, from Nuneaton and Bedworth Borough Council, said they hoped that "any detriment to local residents, businesses and the environment is kept to an absolute minimum".
Smoke plumes could be seen from the M69 in Leicestershire