Raw sewage from 77,000 people is being released into the environment every day without treatment.
It's happening at 36 towns and villages across the country, including Howth. Half of the raw sewage comes from just three areas, Arklow, Cobh and Kilmore Quay.
There are also 21 large towns and cities, including Dublin, where waste-water treatment did not meet EU standards. This is down from 28 the previous year.
The Environmental Protection Agency report also found that there were three beaches where waste water contributed to poor quality bathing waters. They include Merrion Strand and Sandymount Strand.
The organisation says completing upgrade works at the Ringsend treatment plant, which is due to be finished next year, is essential to protect the Lower Liffey Estuary and Dublin Bay.
The EPA says the pace of improvements needed to protect our environment and public health is too slow.
Dr Tom Ryan, Director of the EPA’s Office of Environmental Enforcement says Irish Water must speed up its delivery of key infrastructure;
“Inadequately treated waste water can pollute our environment and is a risk to people’s health. We are seeing repeated delays in providing treatment for many areas and it is not acceptable that 13 towns and villages will still have no waste water treatment by the end of 2021.”