How the EU Bathing Water Directive works
Published May 28, 2026 · ~5 min read
The sea-quality grades you see on Tirkiz are not assigned arbitrarily — they follow a single European framework: Directive 2006/7/EC on the management of bathing-water quality. Here is how it works and what its grades actually mean.
What the Directive governs
Directive 2006/7/EC harmonises how bathing-water quality is monitored and assessed across the entire European Union, both at sea and in fresh waters. It sets out which indicators are measured, how often, and how a final grade is derived from the results. Thanks to this, a grade of “excellent” in Croatia means the same as in any other member state.
Two key indicators
Quality is assessed on the basis of two kinds of intestinal bacteria: Escherichia coli and intestinal enterococci. Their presence is a reliable indicator of faecal contamination, for example from sewage or agriculture. The Directive sets limit values for both groups.
How the grade is calculated
The grade is not the result of a single measurement, but a statistical calculation from a series of samples collected over several seasons — usually the last four years. From this dataset, percentiles of the bacteria concentrations are computed, and the water is sorted accordingly into one of four classes: excellent, good, sufficient or poor. This approach softens the impact of a single bad sample.
Who carries out the measurements in Croatia
In Croatia, sampling and laboratory analyses are carried out by authorised institutions during the bathing season. The results are gathered and published by the Institute of Oceanography and Fisheries (IZOR), from where Tirkiz takes them and presents them more clearly. Tirkiz does not perform its own measurements.
What the grade does not cover
The bathing-water quality grade speaks to the microbiological cleanliness of the sea, not to everything else. It does not measure sea temperature, the presence of jellyfish, litter on the beach, or safety conditions such as currents or depth. For a complete picture, consider that information separately.