Swimmers have taken to the water at Islandmagee to protest against the building of gas storage caverns nearby.
Seven gas caverns are set to be constructed by carving out salt layers under Larne Lough to store half a billion cubic metres of natural gas.
The firm behind the project say it will create jobs and improve energy security by giving a 14-day buffer during periods of peak demand.
Protesters say the caverns would pose a threat to the local environment.
A marine licence for their proposed construction was approved by the Department of Agriculture and Environment (Daera) in October 2021, but is subject to a judicial review brought by opposition groups the No Gas Caverns campaign and Friends of the Earth NI.
The two groups coordinated Saturday’s protest swim at Brown’s Bay in Islandmagee, County Antrim.
The judicial review is due to begin on 2 May.The beach is an officially designated bathing site and generally popular with swimmers year-round, particularly during the summer months.
About 30 swimmers took to the water under cloudy skies and heavy rain just after midday, with a further 20 or so supporters watching on from the shore.
Most of the group stayed in the sea for about 15 minutes.
Ahead of the swim, Lauryn Alexander, who lives locally and organised the event said she wanted to take part and show support for what she described as a “community-wide effort” to oppose the gas caverns.
Analysis: Louise Cullen, BBC News NI Agriculture and Environment Correspondent
Since it was first proposed, the gas caverns project has been controversial.
Supporters say it would create jobs and give Northern Ireland security in the event of a disruption to energy supply.
And they say the concentrated brine produced in making the caverns would disperse rapidly in the sea.
Long-term, the caverns could be used to store hydrogen as a product of surplus renewable energy, maximising our wind power generation potential and making a contribution to reaching Net Zero.
But campaigners say the hyper-saline water released in carving out the caverns threatens vulnerable species in several Areas of Special Scientific Interest along the coast, potentially creating a “dead zone”.
They fear building space for storing gas locks Northern Ireland into fossil fuel infrastructure that would damage Net Zero ambitions.
The controversy shows just how difficult and delicate a balance it is to strike between human and environmental needs.
She said that the beaches of Islandmagee have become a popular attraction for open-water swimmers from “far and wide”, and that Saturday’s swim was about protecting that natural environment which she says the caverns would “ruin completely”.
James Orr, director of Friends of the Earth NI, said that his organisation decided to get involved with the campaign because of the “fantastic community who love their place and have been mobilising for a number of years” and that it felt like a “natural match” for them to support the campaign.
He added that the commitment to this campaign from its supporters was highlighted by the fact that they were willing to “jump in the sea”.
Mr Orr noted that the upcoming judicial review would be an “opportunity to raise a whole range of environmental arguments against this project”.
The groups say they have raised tens of thousands of pounds to fund legal costs for their judicial challenge to Daera’s decision to grant the project a marine construction licence – £5,000 was donated by the non-profit organisation Wild Justice, part-owned by the broadcaster and naturalist Chris Packham.
On 2 April, the protest groups organised a so-called Boots on the Beach event, in which some 200 people marched along Brown’s Bay beach in opposition to the gas caverns.
Opposition to the project is largely based on environmental grounds.
Campaigners say the construction process will involve the pumping of “very salty water” into Larne Lough, creating what they call a “dead zone” in which no animal life can survive.
They also say that drilling will ward off certain marine animals.
As the area is used by the Irish Whale and Dolphin Group to measure marine mammal sightings, they say that the drilling could interrupt a decades-long data set important in tracking the number of these animals.
The marine area in Larne Lough and around Islandmagee has several designated protected areas.
Islandmagee Energy says there will be no long-term damage to wildlife and that any impact created by the discharge of the brine (very salty water) will be localised to a small area at an approved distance offshore away from Larne Lough.
It says the project will not affect any wildlife native to Islandmagee.
Harland and Wolff, Islandmagee Energy’s parent company, said that storage of gas in Northern Ireland “is more important now than ever”.
It said this was “in order to ensure the long-term security of energy supply, which will protect consumers and businesses from volatile movements in the prices of energy, whilst ensuring businesses can continue operating and everyone is adequately supplied at all times of the year”.
In a statement to BBC News NI, it said that the project would create about 1,600 direct and indirect jobs and bring about £400m into the wider economy.
It said it will have a “significant economic and social benefits to Northern Ireland”.
It added that it had “supplied the required documents to the relevant authorities who have issued approvals for the project to proceed, and we believe that we have satisfied or exceeded all of the requirements”.
Deara has previously told BBC News NI that it is not in a position to comment while the issue is an “on-going legal matter”.