A blocked sewer has left raw sewage overflowing into a river that runs through a public park and into the internationally renowned Bull Island nature reserve for the past week.
Irish Water crews are working to resolve the problem in what they have described as a "very complex" operation that will require the emptying of an underground sewage tank before the blockage can be accessed.
Sewage has been entering the Nanekin River through a culvert in a housing estate in Harmonstown, Dublin. The river then flows through St Anne's Park, along community playing pitches and the park's duck pond before entering the Bull Island estuary.
Dublin City Council said the incident was notified to it by a member of the public on February 28 and it had been using sand bags to block off the inlet into the pond.
But the river then flows into the estuary that serves Bull Island where the protected salt marshes and dunes are home to 180 native and migratory bird species as well as rare plants and insects.
Dublin City Council said no deaths of fish or birds had been identified.
The Environmental Protection Agency (EPA) said Irish Water notified it of the incident on March 2 and it was investigating.
"Our priority is to ensure that Irish Water completes the corrective actions needed to unblock the sewer, resolve the incident and protect the environment," it said.
Irish Water said it had notified Inland Fisheries Ireland.
"A blockage suspected to be located in a syphon under the river is the likely cause of this overflow," it said.
"It will be necessary to empty an underground sewage tank so that crews can access the blockage in order to remove it. The health and safety of the crews involved in this work is paramount.
"The situation is ongoing and very complex. It is not possible to divert the sewage.
"We are continuing to work with Dublin City Council to resolve it as quickly as possible."