There are hopes that a new ferry from Greencastle to Carlingford will increase tourism in the scenic area.
The service from the Co Down town across the border will create 18 new full-time jobs and comes following a £8.8m investment by Frazer Ferries Group in Limerick.
New terminals have also been created at Greencastle and Greenore to service the 44-car vessel, which has just completed its maiden passenger voyage.
The crossing takes 15 to 20 minutes, navigating one of the most scenic stretches of water in Ireland, connecting the Mourne coastal route to the Carlingford and Cooley peninsula. The one-mile ferry route will save passengers almost 35 miles and up to 90 minutes by road.
Paul O'Sullivan, managing director of Scenic Carlingford Ferry, said his team is looking forward to welcoming visitors on-board.
"Carlingford Lough is located midway between the two major population centres of Dublin and Belfast," he said.
"Scenic Carlingford Ferry will act as a catalyst for economic development in the south Down and north Louth regions, and will become an essential infrastructural link which will stimulate economic growth in a range of sectors, including tourism."
Frazer Ferries also operates the Lough Foyle Ferry, linking the Inishowen peninsula in Co Donegal on the Wild Atlantic Way with the Causeway coastal route.