Over 90% of rivers checked for markers of E. coli across Ireland tested positive.
It is part of the findings in a study carried out by NUI Galway into the presence of contamination in waterways.
56% of seawaters samples and 75% of lake samples were found to have the disease which causes E. coli.
Professor Dearbhaile Morris, one of the authors of the report, says the findings were generally high.
"We collected samples of sea waters, river waters and lake waters around Ireland and we collected 75 samples in total between December 2018 and October 2019.
"We found that about 65% of samples that we collected tested positive for the presence of genetic markers for this particular type of E. ccoli."
Prof. Morris said that Ireland is worse than the EU average.
"Unfortunately in Ireland we have had the highest instance of human infection with this particular type of E. coli which is called Shiga toxigenic E. coli (STEC).
"We are on average about ten timed higher in terms of our instance rates compared to other EU member states."