River Pollution in Portugal
Rivers in Portugal had an average biochemical oxygen demand of 3.14 mg/L in 2023, 40% above the European average of 2.24, and a phosphate concentration of 0.036 mg/L, 56% below the European average of 0.081.
Data year 2023 · Source: Eurostat, based on European Environment Agency monitoring data (January 2026)
Organic pollution: BOD in rivers
The average biochemical oxygen demand in rivers in Portugal was 3.14 mg of oxygen per litre in 2023, 40% above the European average of 2.24. That is the 19th lowest of the 21 countries with data, where lower means less organic pollution. The figure is almost unchanged since 2007, when it was 3.17.
Nutrient pollution: phosphate in rivers
Phosphate in rivers in Portugal averaged 0.036 mg/L in 2023, 56% below the European average of 0.081. That is the 11th lowest of 23 countries. The concentration has fallen by 18% since 2007, when it was 0.044.
Nitrate in groundwater
Groundwater in Portugal contained an average of 15.7 mg of nitrate per litre in 2023, 13% below the European average of 18.1. The EU limit for drinking water is 50 mg/L. The national average is below that limit, although individual wells can be well above the average. The figure has fallen by 11% since 2007.
How Portugal compares
Countries closest to Portugal when ranked from lowest to highest BOD in rivers. See the full table for Europe, or the CO₂ emissions of Portugal.
| # | Country | BOD (mg/L) | Phosphate (mg/L) | Nitrate, groundwater (mg/L) |
|---|---|---|---|---|
| 17 | Italy | 2.59 | 0.098 | 18.8 |
| 18 | Romania | 3.13 | 0.090 | 15.5 |
| 19 | Portugal | 3.14 | 0.036 | 15.7 |
| 20 | Spain | 3.34 | 0.547 | 31.7 |
| 21 | Kosovo | 12.49 |
What these measures tell you
Biochemical oxygen demand (BOD)
BOD is the amount of oxygen that microorganisms need to break down the organic matter in a water sample over five days. High values point to organic pollution, usually from sewage, farm run-off or industrial wastewater. They also mean less oxygen is left for fish and other river life.
Phosphate
Phosphate is a nutrient that reaches rivers from fertilisers, sewage and detergents. Too much of it feeds algae, which can choke rivers and lakes and strip oxygen from the water.
Nitrate in groundwater
Nitrate comes mainly from fertiliser and manure that seep through the soil. It is measured in groundwater, which feeds rivers and supplies much of Europe’s drinking water. The EU limit for drinking water is 50 mg of nitrate per litre.
Frequently asked questions
How polluted are rivers in Portugal?
Measured by biochemical oxygen demand, rivers in Portugal averaged 3.14 mg/L in 2023, 40% above the European average of 2.24 mg/L. Phosphate averaged 0.036 mg/L.
Is river water quality in Portugal improving?
BOD in rivers is almost unchanged since 2007. Phosphate in rivers has fallen by 18% since 2007. Lower values mean less pollution.
Is nitrate in groundwater a problem in Portugal?
The national average was 15.7 mg/L in 2023, below the EU drinking-water limit of 50 mg/L. An average can hide local hotspots in farming areas.
What is BOD in water?
Biochemical oxygen demand is the oxygen microorganisms use to break down organic matter in water over five days. Higher values indicate more organic pollution, typically from sewage or farm run-off.
About the data. Each figure is a national average across the river or groundwater monitoring stations a country reports to the European Environment Agency. It describes rivers in general, not any single river, and countries differ in how many stations they report. Not every country reports every measure.
Source: Eurostat datasets Biochemical oxygen demand in rivers, Phosphate in rivers and Nitrate in groundwater, updated January 2026. Latest year available: 2023.
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