The EPA has identified the Midlands as having the most significant rise in nitrate concentrations.
Offaly is among the top ten counties with the greatest decline in water quality level.
The EPA's latest water quality report looked at just over 2,400 rivers in Ireland from 2019 to 2024, with just under 200 of these in the Midlands.
Around 16 river bodies declined in quality, with only 5 improving their status.
In Laois 14 saw a drop in water quality, while 8 improved, while Westmeath 10 declined, and 7 improved.
The report also notes the highest increase in nitrate concentrations is in the Midlands.
Dr. Eimear Cotter, Director of the EPA's Office of Evidence and Assessment, says there are a number of causes:
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