The Environmental Protection Agency has said it has repeatedly highlighted that the Ringsend Wastewater Treatment Plant is failing to meet national and European Union treatment standards.
In a statement, the EPA said the plant is failing to meet these standards and failing to comply with the requirements of its wastewater discharge licence because the plant is not big enough to adequately treat all of the wastewater that it receives.
Wastewater discharged back into the environment from this overloaded plant is breaching, and will continue to breach, the quality standards until upgrade works are complete, it said.
Speaking on RTÉ's News at One, a senior scientist with the Environmental Protection Agency, Noel Byrne, said the Ringsend plant is not large enough and is in breach of national and EU treatment standards.
Plans are in place to expand the facility by 2023, he said.
Mr Byrne confirmed that an EPA inspector is being sent to the Ringsend Wastewater Treatment Plant to assess the situation at the facility.
It comes as drone footage emerged of what appears to be discolouration of the water at the discharge point.
In a statement issued earlier today, Irish Water confirmed that no incidents had occurred at the Ringsend Wastewater Treatment Plant in the last 48 hours.
The statement went on to say that the plant is operating normally, and that the wastewater is treated to the best possible standards currently achievable at the plant.
"Factors such as low tidal levels, temperature of the receiving waters, the volume of wastewater discharged and wind strength and direction can increase the visibility of the treated effluent at the discharge point," it said.
The Irish Water statement also said that discolouration of the water at the discharge point may be visible on occasion "until upgrade works are completed as the plant is currently overloaded".
The company says that the plant treats around 40% of the country's wastewater load, and that €400m is being invested in the staged upgrading of the Ringsend facility.
In its statement the EPA said Irish Water informed it today of a brown-coloured plume that was photographed discharging from the wastewater treatment plant.
It said Irish Water reported no unusual occurrence or breakdown at the plant over the last 48 hours and it is currently investigating the cause of the plume.
The EPA said the plant has a capacity to treat waste water from a population equivalent of 1.64 million. The load entering the plant is from a population equivalent of approximately 2.3 million.
Additional treatment capacity of 400,000 population equivalent is under construction, with a completion date of 2020, and further improvements to bring the treatment capacity up to 2.4 million will be completed by 2023.
The EPA said it is continuing to liaise with Irish Water in relation to this issue. However, it is likely the problems with the discharge will continue at this overloaded treatment plant until the upgrade works are completed, between 2020 and 2023.
This means that there may be a discoloured plume visible from time-to-time until the plant is upgraded.
Local authorities are responsible for managing bathing waters and they will also have information on the latest water quality.