Untreated sewage is being dumped into the sea and rivers at 43 locations across Ireland.
The Environmental Protection Agency says 29 larges towns and cities around the country have failed to meet EU standards.
The report suggests the problems are due to a lack of investment in infrastructure which has dropped by 40 percent, in the last decade.
It also found the building of treatment plants in many areas have been delayed by up to two years.
Juliette Gash reports;
