Raw sewage is flowing into the environment from 35 towns and villages every day - including Killala and Newport.
That's according to a new report from the Environmental Protection Agency, which has also highlighted 113 locations country-wide where Irish Water needs to prioritise wastewater treatment to protect public health and the environment.
The annual report for 2019 published this morning also highlights 19 large towns and cities, including Dublin and Cork, that have failed to meet EU standards to prevent pollution.
The Sligo towns of Ballymote and Tubbercurry are also on that list.
The EPA says raw sewage discharges pose an unacceptable risk to the environment and public health.
The Mayo towns of Killala and Newport are included in the list of 35 towns and villages where raw sewage is released into the environment.
However, the new wastewater treatment infrastructure is now in place in Killala, and was due to commence operations in the final quarter of this year.
And Irish Water says it's progressing plans for a new waste water treatment plant in Newport.