As Hinkley Point C power plant is being built in South West England, hundreds of thousands of fish living in the Severn estuary, including protected Atlantic salmon, may be under threat from the plant’s cooling turbines.

An acoustic deterrent could help deflect fish away from the water intakes. Developed by Fish Guidance Systems Ltd, the Sound Projector Array would use underwater sound projectors to prevent fish being drawn.

Hinkley Point C’s owner, the energy company EDF, would prefer to proceed with a change to the Secretary of State’s Development Consent Order that requires the device. Although they originally proposed the installation as part of the environmental protection package, the company is now proposing to avoid it.

According to some scientists, however, removing this piece of environmental protection would threaten the biodiverse ecosystem of the UK’s largest estuary and designated Special Area of Conservation. It could also set a precedent for future projects like Sizewell nuclear power stations in Suffolk.

“I have lost sleep over the danger to the fish and the risk of devastating the ecosystem of the Severn estuary,” a researcher in coastal governance, Natasha Bradshaw, said. “There is little proof that fish will survive the journey through 3 km of tunnels or what impact returning them (dead or alive) into the estuary will have on the ecosystem.”

The Severn estuary supports up to 110 fish species, with fish nurseries serving the whole of the Bristol Channel and Celtic Sea, and an average of 74,000 wintering birds each year.

“In such a large and complex ecosystem, effects of individual projects are always difficult to pinpoint. The situation is complicated further by ongoing changes wrought by climate change,” says David Lambert, managing director of Fish Guidance Systems. “The provision of an acoustic fish deterrent as required under the existing Development Consent Order is to mitigate the uncertainty over these impacts which will perpetuate through the 60 year lifespan of the plant.”

EDF, on the other hand, wants to build fish protection measures like low velocity side entry water intakes designed to minimize the number of fish taken into the system and a fish return system.

They said that “installing and maintaining dozens of sound projectors underwater two miles offshore is dangerous and poses risks to divers that are unacceptable to Hinkley Point C” and that data shows the new power station will have negligible impact on the fish populations anyway.

“The impact of the power station is tiny in comparison to the impact of commercial fishing,” a spokesperson for EDF said. “All power station cooling systems using river or sea water have an impact on fish. Even with measures to protect fish, not all will survive the passage through the cooling tunnels. The fish return system is effective for more robust species.”

To that, Lambert responds for instance that EDF doesn’t take account of “the fact that technology has moved on considerably in the last few years, and systems have now been designed to operate in the conditions of the Severn Estuary” and “how climate change and other external factors might alter the characteristics of fish stocks over the 60 year operating life of the station”.

Hinkley Point C will be generating electricity from 2025 and, meanwhile, the debate is open.

“Of the over one hundred consultation responses received from individuals and conservation bodies by the Environment Agency regarding the application to remove the requirement for an acoustic fish deterrent, Fish Guidance Systems are not aware of one response that agreed with the removal,” Lambert adds.

The Environment Agency and the Marine Management Organisation are carrying out separate consultations on the applications sent by EDF.

Secretary of state for Business, Energy and Industrial Strategy Alok Sharma is responsible for a decision that is currently imminent.