It found just 20 of Ireland's rivers have pristine conditions - down from more than 500 in the 1980s.
Roughly half of the country's coastal waters, rivers and lakes have unacceptable levels of pollution.
A new report from the Environmental Protection Agency shows only 53% are of satisfactory quality.
It highlights our river waters as a particular concern, with the quality having dropped by 5.5% since the last assessment four years ago.
EPA Water Programme Manager, Mary Gurrie, says the poor water quality is down to a number of factors:
According to the EPA, the quality of water in Irish rivers is getting worse.
It found just 20 rivers have pristine conditions - down from more than 500 in the 1980s.
Ms. Gurrie says agriculture and urban wastewater are the main contributors:
Meanwhile, the number of seriously polluted rivers has increased from six to nine in the past three years.
In the midlands, 24% of rivers in Laois are of high quality - that's 4% in Offaly - while none of the rivers in Westmeath are of high quality.
However, 13% of lakes in Westmeath are high quality, with 75% rated as good.
Water Programme Manager, Mary Gurrie, adds it's important steps are now taken to clean-up our waterways: