The Environmental Protection Agency says "it's unacceptable" that raw sewage is entering rivers and bathing areas.
The EPA says it's found that waterways in 42 locations around the country are being put at risk of pollution because of the lack of waste water treatment plants.
They include Bundoran in Donegal, which is now the subject of EU legal action.
Inadequate infrastructure is also noted in Falcarragh. Moville, Kilcar, Ramelton and St Johnston.
Over a quarter of large urban areas did not meet mandatory EU safety rules, including Letterkenny and the Twin Towns.
The EPA's Programme Manager David Flynn says Ireland's tourist hotspots are being put at risk...........