The Environmental Protection Agency is sending an inspector to assess Dublin's only wastewater treatment plant.
An aerial video being shared online appears to show brown-coloured water being pumped out of Ringsend into Dublin Bay.
The video was taken on Monday evening.
Irish Water contacted the Environmental Protection Agency this morning about the plume.
However, the company has said the plant is treating water to the "best possible standards currently achievable".
"Irish Water can confirm no incidents have occurred at the Ringsend Wastewater Treatment Plant in the last 48 hours", it said on Tuesday morning.
An inspector from the Environmental Protection Agency will take samples from the discharge.
Last week, a swimming ban was issued for 4 Dublin beaches after an overflow at the plant, which Dun Laoighaire Rathdown Council blamed on heavy rain.
Another Ringsend Leak?
The Ringsend plant has been working over capacity for years, and has to process about 40% of the entire country’s wastewater.
Work on a €400m upgrade and extension has begun, but even that won't solve the capacity issue.
There have been ongoing talks about building a second treatment plant on the north side of Dublin.
However, there have been thousands of objections the proposed site in Clonshaugh.
Irish Water explained that discoloured water may be visible at Ringsend's discharge point until the €400m upgrade is finished.
It said factors including low tides, temperature and wind strength "can increase the visibility of the treated effluent".
