What the sea-quality grades mean
Published May 23, 2026 · ~4 min read
Every beach on Tirkiz carries a sea-quality grade — by colour and by word. That grade is not a live reading of temperature or of the cleanliness you can see with the naked eye; it is a summary of laboratory analyses of the seawater, following European Union rules. Here is how to read it.
The four grades
Bathing-water quality is sorted into four classes. The higher the grade, the more consistently the sea showed low pollution levels through the season.
- Excellent — the water is generally free of pollution; the top category.
- Good — quality is high, with occasional mild deviations.
- Sufficient — the water meets the minimum required standards, but falls below the higher classes.
- Poor — measured values exceed the permitted limits; caution is advised.
What is actually measured
The grade is based on the concentration of two kinds of intestinal bacteria in a seawater sample: Escherichia coli (E. coli) and intestinal enterococci. These are not necessarily harmful in themselves, but they are a reliable indicator of faecal contamination — for example from sewage or stormwater outflows after heavy rain. The limits and the classification method are set by EU Directive 2006/7/EC on the management of bathing-water quality.
A single reading vs the seasonal grade
It is important to distinguish two things. A single reading shows the state on the day of sampling at one sampling point. The seasonal grade is a statistical calculation from all samples collected during the season, and usually several earlier ones too. That is why a beach with one elevated reading can still hold an excellent seasonal grade — one bad sample does not undo a run of good ones.
How fresh the data is
Measurements are taken during the bathing season, roughly from mid-May to late September, in cycles of about two weeks. Tirkiz pulls the data from IZOR every few hours and shows, next to each beach, when it was last refreshed. Outside the season there are no new samples, so the page shows the last available seasonal grade and clearly marks that the bathing season is not active.
How to read a beach page
On every beach page the grade is highlighted at the top, coloured according to its quality class. If the data is more than half a day old, a data-age badge appears. When the season is not active, instead of a staleness warning the page shows a notice about the season status and the expected start of the next one.