The Environmental Protection Agency says 29% of Irish rivers are still polluted to varying degrees despite improvements in water quality during recent years.
In its latest report on water quality, the agency also says 66 lakes and 15 estuaries are not up to standard.
The report assesses the quality of lakes, rivers, canals, coastal areas and groundwater.
The EPA says the main contributors to water pollution continue to be discharges from municipal waste treatment plants and agricultural run-off.