When you see "Water Quality: Excellent" on a sign at a beach, what does it really mean? Who issues the rating, how is it calculated, and where can you check up-to-date data? This guide explains it all.
Who classifies water quality in Portugal?
The body responsible for monitoring the quality of bathing waters in Portugal is APA — the Portuguese Environment Agency. Working with the regional water authorities (ARH), it collects samples at beaches throughout the bathing season and publishes the results on the InfoÁgua portal (infoagua.apambiente.pt).
What is measured?
The main microbiological indicators are:
- Intestinal enterococci: Faecal bacteria that indicate sewage contamination. Threshold for "Excellent": ≤ 100 CFU/100 ml.
- Escherichia coli (E. coli): Another faecal contamination indicator. Threshold for "Excellent": ≤ 250 CFU/100 ml.
The four classifications
The European Bathing Water Directive (2006/7/EC) defines four classifications, used in Portugal:
🟢 Excellent
Enterococci and E. coli levels are well below safety thresholds. This is the best possible rating and indicates water with excellent bathing conditions and no known health risks.
🟡 Good
Water quality is good and bathing is safe. Microbiological levels sit within acceptable parameters, though not as low as in "Excellent".
🟠 Sufficient
The legal minimum for the beach to remain open to the public. Some years may show higher values. People with compromised immune systems should be cautious.
🔴 Poor
The beach does not meet the minimum requirements. When a beach is rated "Poor" for four consecutive years, a bathing ban is mandatory. Avoid bathing at beaches with this rating.
How is the annual classification calculated?
The rating does not come from a single sample but from a four-year profile. The values are assessed using the 95th percentile of enterococci and E. coli measurements collected over the previous four years.
This means a beach can have one summer with higher values (after heavy rainfall, for example) but still hold an "Excellent" rating if the previous years were clean.
Where to check up-to-date data
- APA InfoÁgua: infoagua.apambiente.pt — real-time data during the bathing season (1 June to 30 September).
- Guia de Praias: every beach profile shows the most recent classification and the year-on-year history.
- On-beach signs: During the bathing season, the classification must be on display at the lifeguard station.
What can temporarily affect quality?
Even beaches rated "Excellent" can have temporary episodes of poorer water quality:
- Heavy rainfall: Washes contaminants into rivers and the sea.
- Algae: Can cause irritation but are not picked up by the microbiological classification.
- Nearby wastewater plants: Failures at sewage treatment works.
In these cases the local authority can issue a temporary bathing ban regardless of the annual rating.
