Firefighters were called to a site at the centre of a outbreak of a fly problem in Oswaldtwistle after 100 bales of waste went up in flames.
Lancashire Fire and Rescue spokesman John Taylor said they are still looking into whether the fire was started deliberately.
Sixteen firefighters from Hyndburn and Rawtenstall were called to the site off Nook Lane and used aerial ladder equipment to help put out the fire at around 2.15am on Thursday, August 2 and create a fire break to stop the fire spreading.
Police, Hyndburn council and Environment Agency officers also attended the scene at the former NIPA laboratories site.
Mr Taylor said: "We were called to the NIPA laboratories site where there were big black bales of rubbish on fire.
"Three fire crews attended the scene and used an aerial ladder to jet water onto the fire.
"They then made sure the squirted water, which would have been polluted by the burning products, did not go into any water courses, brooks or streams."
Deputy council leader Clare Pritchard, who attended the scene with ward councillor Peter Britcliffe, said they are ‘determined’ the fire won’t stop the rubbish being cleared.
She said: "The good news is the rubbish is continuing to be cleared and the number of wagons coming to clear the rubbish has increased.
"Because the rubbish is still on fire they are creating a fire break around it to stop if spreading.
An Environment Agency spokeswoman said they will be supporting fire crews to find out the cause of the fire.
She said: "Thanks to our officers’ quick action, fire water was prevented from entering the local brook.
" The Environment Agency is working very closely with the Fire and Rescue Service and has deployed officers out on site to provide advice and guidance to ensure damage to the surrounding environment is minimised as much as possible.
"We recognise the ongoing concerns of the residents in relation to this site. We would like to re-assure them that we are taking this situation very seriously.
"We are continuing our investigations and will keep them informed of developments throughout the day."