A £100m contract to replace the main sewers in central Belfast has been awarded by the government.
Belfast city centre's sewage system is to be updated
The work is to be carried out by tunnelling contractor Morgan Est in a joint venture with Northern Ireland company Farrens Construction.
The project involves the construction of a new six-mile tunnel up to 13ft in diameter, which is 98ft below the surface in places.
The work is to begin immediately and will take three years to complete.
Katharine Bryan, chief executive of the Water Service, said: "The £100m Belfast Sewers (Tunnel) Project, funded through the Reform and Reinvestment Initiative, represents one of the biggest infrastructure investments in the city.
"It will dramatically improve the current sewerage system and provide Belfast with the modern infrastructure required to cater for the present and future development needs of the city."
Many of the existing sewers in the Belfast area date from the Victorian era and the scheme will significantly improve the water quality in the Lagan and Blackstaff Rivers, reduce the risk of flooding in the Belfast area and ensure compliance with stringent EU environmental standards, she said.