The Government has launched an investigation into an oil spill in Poole Harbour after MPs raised concerns for sensitive nature reserves and the impact of local fisheries.

Poole Harbour Commissioners (PHC), which regulates activities in the harbour, said a leak occurred at a pipeline operated by gas company Perenco, under Owers Bay, on Sunday.

Approximately 200 barrels of reservoir fluid were released after the leak occurred at the Wytch Farm oil field.

Perenco said a “small” amount of reservoir fluid (consisting of 85% water and 15% oil) escaped from its pipeline.

Sightings of oil in Poole Harbour following the pipeline spill are “down by 60-70%” as a clean-up plan has been put in place to protect the area’s wildlife and habitats.

But the public is still being advised to avoid going into the water or using the beaches despite the oil appearing to begin to disperse.

In an urgent question in the Commons, Richard Drax, Conservative MP for South Dorset, said the spill was “potentially catastrophic” but added he had received assurances that it is “not as serious as first thought”.

He told MPs the impact on the marine environment “is unknown” and asked the Government “to ensure that it is paramount the regulator carries out a full investigation into why the leak occurred”.

He said he wanted the Government to seek assurances from Perenco “that the rest of their network is being properly maintained and checked, we do not want this to happen ever again”.

Environment minister Rebecca Pow told the Commons: “Investigations are currently under way to determine the reason for the fault and to make sure that similar incidents are not repeated.

“This has been designated as a tier two incident. If it were to escalate to a tier one, the (Maritime and Coastguard Agency) would lead the response… however, we consider that unlikely due to the rapid response and deployment of the oil mitigation plan.”

She said: “The current situation appears to be stable, with the continuing focus of the strategic co-ordination group to gather further data to assess the environmental implications and to continue to progress a clean-up operation.”

Conservative Sir Robert Syms (Poole) also raised questions over maintenance and compensation for fishermen if the leak led to problems for their catches and Ms Pow replied that she would be in contact with the fisheries’ minister.

PHC carried out a survey of the harbour on Monday morning involving 100 people, helicopters and drones.

It said it was working with local authorities to monitor and clean up the spill using the Shoreline Clean-up and Assessment Technique (Scat).

The authority warned against bathing in the area and said anyone feeling unwell should contact their GP.

It stated: “It is unlikely that there will be any long-term health effects from short exposures (eg days).”

According to Poole Tourism, Poole is Europe’s largest natural harbour and a site of nature conservation, with many international protections in place.

The harbour is also a Ramsar site which recognises wetlands of international importance, particularly for wildfowl, a Site of Special Scientific Interest (SSI) and a Special Protection Area (SPA).

Franck Dy, Perenco UK’s Wytch Farm general manager, said: “Any spill is an extremely serious matter and a full investigation will be launched to ascertain what happened in Poole Harbour.

“It is important to stress that the situation is under control, with the discharge of fluids having been stopped and the spill is being contained.”

Philip Broadhead, leader of Bournemouth, Christchurch and Poole Council, told BBC Radio 4: “I am clearly angry and disappointed, this is the second-largest natural harbour, award-winning beaches, very delicate ecosystem. The natural reaction is to be very worried.”

While we don't know the full extent of the leak yet, a spill in Poole Harbour raises particular concerns

Environment groups have expressed anger and concern at the risk posed by oil facilities on the UK coast, particularly close to protected wildlife sites.

A small protest was held on Monday afternoon with demonstrators unfurling a banner stating “end fossil filth”.

Richard Hill, from the Marine Conservation Society, said: “I am shocked and saddened to see yet another oil spill in UK waters. We need better protection for sensitive sites such as Poole harbour.”

Dr Malcolm Hudson, associate professor in environmental science at the University of Southampton, said the spill was “potentially a serious environmental incident”.

He said: “While we don’t know the full extent of the leak yet, a spill in Poole Harbour raises particular concerns. It’s a very large enclosed bay – and so pollutants may not be flushed out quickly by the tides.”