The Environmental Protection Agency (EPA) has reported that average nitrogen concentrations across 20 'representative sites' increased by 16% in the first half of the year compared to the same period of 2024.

The data was included in the EPA's early insights nitrogen concentration indicator report.

The reports were developed to provide an update on nitrogen concentrations in the major rivers of Ireland on a rolling six-month basis.

The latest report provides nitrogen concentration data from the first six months of 2025 at 20 river monitoring stations, which are located at the most downstream available sites on the major rivers in Ireland, the EPA said.

This report updates the nitrogen concentration profile to include data for January to June 2025, inclusive. Comparisons are made with the same six-month period in previous years for context.

The latest data indicates that nitrogen concentrations have increased by 16% in the first half of 2025 at those sites, relative to the corresponding six month period in 2024.

The EPA said that, year-on-year, nitrogen concentrations fluctuate due to source loading, agricultural land management and weather patterns.

The agency said it is investigating the drivers that have caused these changes over time.

According to the EPA, the six month nitrogen figures have, in previous years, been a "reasonable, albeit conservative predictor" of the overall 12 months.

This early insights update shows the most up to date available information and represents a six-month "snapshot in time", the EPA said.

The EPA reports on catchments requiring nitrogen load reductions to meet water quality objectives.

These reports use three years of nitrogen concentration data at representative sites, the most recent of which covered theperiod 2022 to 2024.

According to the EPA, there was a marked difference in average concentrations between catchment areas mainly located in the east, south and southeast, versus catchments in the west and northwest.

The EPA said this reflects differences in farm practices, soil type and climate conditions.

However, the EPA said that in both geographical groups of catchments, average nitrogen concentrations increased in the first six months, according to the latest data.