Just half of Ireland's sewage is treated to European Union standards - well below the EU average of 90%.
The Environmental Protection Agency's report on Urban Waste Water Treatment for last year also shows poorly treated sewage continues to harm the quality of rivers and lakes.
The watchdog also highlights the largest treatment plant, at Ringsend in Dublin, is overloaded and fails to treat sewage to the required standards.
The report also found more than 30 towns and villages released raw sewage into the environment every day in mid-2022 because they did not have treatment plants.
It shows 12 large towns and cities did not meet wastewater treatment standards to protect the environment. These areas generate half of Ireland's wastewater.
