POLICE are investigating the possible source of a major oil spill in an eight-mile stretch of the River Aire near Castleford.
About 5,000 gallons of diesel, worth thousands of pounds, leaked into the River Aire in Leeds on Saturday night.
The Environment Agency said the oil had covered the stretch of river from bank to bank between Leeds and Castleford.
It is thought that the spill was caused by thieves attempting to steal diesel from an oil tank.
West Yorkshire Police confirmed that officers were investigating the theft of a large amount of diesel from a business on Millshaw Park Industrial estate in Leeds.
Environment Agency officials said they were alerted to oil flowing into the River Aire between 5.40pm and 7.40pm on Saturday. They initially appealed for businesses to check oil and fuel tanks in case a broken pipe or a leak had caused the problem.
Mark West, Environment Agency team leader, said: “It’s too soon to be absolutely certain, but we have been working closely with the police, and have found a very strong lead.
“We’re continuing to investigate and the company involved is co-operating fully. We believe around 5,000 gallons of oil has leaked into the river from the oil tank. What this underlines is the responsibility businesses have to safeguard their fuel tanks under the oils storage regulations.”
Contractors and staff from the agency and the Canal and Rivers Trust (CRT) had to use absorbent booms and pads to soak up the oil on Monday and Tuesday.
Stephen Hardy, communications manager at CRT, said: “It was a big spill, much larger than we are used to dealing with, it is certainly quite an unusual situation, something like this doesn’t happen every day.
“We have completed the clean up, considering the size of the spill it’s gone very well, the majority of the diesel has been mopped up using absorbent pads, and we also pumped some out into tankers.
“We would continue to advise people not to let their dogs drink from the river as a precaution.
“So far we have not had any reports of implications for wildlife, which is good.”
An Environment Agency statement said: “The sheer quantity of oil in the fast-moving waters of the river and canal system means that a large part of it will be flushed downstream into the Humber. By this time it will be very dispersed and the risk to the environment will be greatly reduced.”
A West Yorkshire Police spokeswoman said inquiries were ongoing.