Nitrogen levels in Ireland’s rivers have increased by 16% during the first six months of this year when compared to the same period in 2024, the Environmental Protection Agency (EPA) has found.

The EPA’s Early Insights Nitrogen Indicator report for the first half of 2025 shows that the average total oxidised nitrogen (TON) level in the country’s rivers was in excess of 9mg/l of NO3 compared to 8mg/l in 2024.

The guideline value to support healthy river systems is 8mg/l of NO3 and 11.5mg/l for estuaries.

“Year on year, nitrogen levels fluctuate due to source loading, agricultural land management and weather patterns. The EPA is investigating the drivers that have caused these changes over time,” the EPA stated.

“Nitrogen remains too high in the southeastern half of the country and further action will be needed to reduce concentrations to levels that support healthy ecosystems,” the EPA claimed.

The environmental agency said agriculture remained “the primary source of nitrogen in our waters”.

“While significant work is underway in the sector, the scale and pace of action needs to increase,” the report stated.

Commenting on the report, the EPA’s Dr Eimear Cotter said the increase in river nitrogen levels was “disappointing” and she called on the farm sector to “implement sustained actions to reduce nutrient losses in a targeted way”.