THOUSANDS of litres of oil have leaked into Exeter's Ludwell Valley Park from the grounds of the Royal Devon & Exeter Hospital, Wonford.
The spill went undetected for some time and was caused by a broken underground fuel line in the grounds of the hospital.
The hospital, which is to switch to gas boilers from October to prevent a recurrence, has appointed specialist contractors to work with the Environment Agency to minimise the impact of the leak.
The leak came to light after the Environment Agency received numerous reports from concerned members of the public about a "strong odour" and "oily sheen" in a stream flowing through Ludwell Valley Park.
The pollution was coming from a surface water outfall in the park and absorbent booms and pads were deployed to soak up the oil, but the spill continued and mechanical equipment had to be brought in to remove oil from the stream.
The source of the oil was traced to the hospital which immediately appointed firms of specialist consultants and contractors to stop any further leaks and to install a temporary fuel storage system while a full investigation was carried out.
Cliff Barnes, deputy director of Strategic Capital Planning at the RD&E, said: "We are grateful to the Environment Agency for bringing this matter to our attention. As soon as we were alerted to this leak we took prompt action and within 24 hours we had mitigated the risk to the stream and park users.
"We have now decided to replace all oil-fired boilers to the residence blocks with gas so that this type of accidental leak can never happen again."
Lesley Robson, city councillor for Priory, praised the hospital for its swift response.
Cllr Robson said: "I really would like to thank them for dealing with this so promptly."
It is believed most of the oil that leaked has permeated into the ground, but some found its way into the surface water drainage system – and it was this that was seen by members of the public in the stream in Ludwell Valley Park.
The clean-up operation involves remediating the site to minimise any further impact to the stream and environment.
Chris Sargent for the Environment Agency, said: "We have formally warned the hospital about the incident and will seek to recover the cost of investigating the pollution. We will work with the hospital to improve practices and reduce the risk of this happening again."