Irish Water says they're working to repair pumps at Ringsend Wastewater Treatment Plant after a mechanical breakdown.
The utility confirmed a 'low level incident' at the plant.
They're warning of an increased risk of stormwater overflows in the coming days while repairs are carried out.
Irish Water said: "Crews are on site working to carry out essential repairs to the pumps as quickly as possible in order to allow the plant to return to its full treatment capacity.
"Irish Water have notified the Environmental Protection Agency Dublin City Council and Dun Laoghaire-Rathdown County Council of this incident."
This year saw several beach closures in Dublin Bay due to overflows from Ringsend.
The treatment plant almost always operates at above what it was designed to.
To cope with demand, it's getting a €400m upgrade and extension.
Irish Water is also looking for permission to build a second treatment plant on the north side to share the load.