Poole Harbor Commissioners (PHC) said the leak occurred on a pipeline operated by French-British company Perenco.
In a press release, Perenco UK described the leak as “limited”, and said it was “working closely with the relevant authorities and a clean-up operation is underway”.
“A full investigation will be launched to determine exactly what happened at Poole Harbour,” said Frank Dye, managing director of Perenco UK.
“The situation is under control,” he said.
The Wich farm, which has been in operation since 1979, is one of the largest onshore oil fields in Europe. North Sea Shell Survey brings out volunteers.