Regular sampling and testing of sea quality on Croatian beaches starts at the beginning of May. Samples are tested every 15 days and the updated results are announced regularly. The sea quality is measured on 203 beaches in Istria, and analyses up to now show a high sanitary cleanliness level.
Based on years-long experience of testing the sanitary cleanliness level of sea on beaches internal criteria have been introduced, so that there are four levels and corresponding colours: sea of high sanitary cleanliness level (blue), sea of good sanitary cleanliness level (green), moderately polluted sea (yellow) and polluted sea (red). The aim of introducing these criteria is to point out the areas with very clean sea.
Important factors for grading are colour, transparency, visible waste matter, visible mineral unctuousness, but also pH value and sea temperature. The sea quality on beaches of the entire coastal area and islands has been measured since 1988.