36 towns and villages across the country are releasing raw sewage into the environment everyday.
The Environmental Protection Agency says half of the raw sewage comes from just three areas - Arklow, Cobh and Kilmore Quay.
Mayo areas highlighted in the report include Newport and Killala, while in Galway there’s Roundstone, Spiddal, Carraroe and Ahascragh.
Waste water treatment in 21 of Ireland's 169 large towns and cities did not meet national and European standards.
Andy Fanning from the EPA says Irish Water needs to do more to address the country's waste water treatment infrastructure.
Irish Water has welcomed the report and says it's making an "unprecedented" investment in treating waste water.
It plans to spend some 400 million euro building treatment plants next year - up from 240 million euro last year.
Seán Laffey, head of asset management at the utility, says it's making good progress.