CAMPAIGNERS on both sides of the border are objecting to plans to deposit dredged material within Carlingford Lough, claiming it would bring nuclear substances into the bay.
Warrenpoint Port is proposing moving the placing of material collected during its regular dredging - carried out in order to maintain clear access for vessels - from 16 miles out at sea to within the lough.
The port has earmarked a site between Greencastle and Cranfield for the plans.
The Carlingford Ferry crosses close to the proposed zone, from Greencastle in Co Down to Greenore in Co Louth.
Christine Gibson, from Greencastle Keep It Green, said: "We have major concerns about the nuclear and radioactive substances in the lough and how this is going to be dredged and dumped at Greencastle - which is a designated site for its wildlife and natural assets."
"We are concerned about coastal erosion and how it will affect our air and water quality," she told the BBC.
However, CEO of Warrenpoint Port, Clare Guinness, said: "We are not aware of any nuclear content anywhere in the Lough and nor are there any plans to have any."
Ms Guinness said the dredging is "heavily regulated" and added that there is "frequent surveying" of material collected.
"As the chief executive of a business with a large substantial cost like that, that is increasing every year, it is only right that we look at doing it in a more efficient way."
Biologist Breffni Martin believes the plan is linked to Brexit.
"The thinking could be that, after Brexit, the European designations could disappear.
"It is hard to understand given the protections that are there, why Warrenpoint would go ahead with this, because in a European framework it seems unlikely that it would be approved," he added.