Irish Water says the impact of the latest sewage spill into Dublin bay will be "temporary".
Eight beaches, from Dollymount on the north side to White Rock on the south side, have been closed to swimmers.
It's after sewage from the water treatment plant in Ringsend overflowed during a low-level warning for rain earlier this week.
Sean Laffey from Irish Water hopes some of the beaches will re-open to swimmers once the results of tests come back.
"The discharge goes out with the tide, and the tide goes in and out twice a day so any impact it will have will be very passing in nature".
Dublin Beach Closures
At the moment, there are eight beaches that are closed to swimmers because of dirty water. They are:
- The Forty Foot
- White Rock
Sandymount and Merrion beaches will not re-open following this week's tests. They are closed to swimmers long-term because of general water quality.
Ringsend Leak Problems
There have been a number of sewage spills from the Ringsend treatment plant recently.
Back in February, thousands of tonnes of partially treated sewage flooded into Dublin Bay.
It took three days for Irish Water to inform the public there was a potential risk to their health.
At the time, Irish Water promised to improve its communications.
The Ringsend 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.