(Bloomberg) -- A clean up is underway in the UK’s Poole Harbour where an oil spill could threaten rare birds at a nearby nature sanctuary.

Poole Harbour Commissioners said about 200 barrels of reservoir fluid had leaked from the Wytch Farm oil field in southern England into the bay. 

Wytch Farm is the largest onshore oil field in western Europe, with estimated reserves of almost half a billion barrels, according to the British Geological Survey. It’s located less than three miles (4.8 km) from protected coastal areas that are an important habitat for bird species including the spoonbill, avocet and osprey.  

Perenco SA, which operates a pipeline at the field, confirmed a “limited leak” at one of its well sites. It said in a statement the leak had been stopped and booms deployed to contain the slick as clean-up efforts got underway.

Wildlife experts said that, while limited in size, the spill was worrying because many birds are reliant on the area for food. Breeding seabirds are currently gathering there to roost while migratory birds are stopping off to feed on their way north. 

The Royal Society for the Protection of Birds, a conservation charity which manages two nature reserves surrounding the bay, said it was “very concerned.”  

“The area is home to numerous bird species such as Black Headed Gull, Mediterranean Gull, Redshank and Oystercatcher which breed on the coastline, and many other waterbirds which rely on the harbor mudflats for food,” Peter Robertson, senior site manager, said. 

Local conservation projects include a program to attract the osprey back to the area after it became locally extinct 180 years ago. A pair currently resident in the bay feed almost exclusively on fish from its waters during the spring and summer, according to local charity Birds of Poole Harbour. 

Other affected wildlife may include bass, which breed in the bay, seahorses, molluscs and seals, Dorset Wildlife Trust, a nature charity, said in a statement on its website. 

Poole Harbour Commissioners said the public should avoid the water and beaches. 

Perenco said it was investigating the cause of the leak from the pipeline beneath Ower Bay, on the south side of the harbor.

Rebecca Pow, a minister in the environment department, told the UK parliament an investigation would examine inspection and maintenance records but rejected calls for a wider review of oil sites close to nature-rich areas.

“This oil field has been worked since 1979 and this is the first incident of any kind that has occurred,” she said, adding that the fluid released was 80% saline solution and 20% crude oil.

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