Why are Baltic bathing sites being closed? It is not always cyanobacteria to blame

In the middle of the holiday season, many bathing sites along the Baltic coast are flying a red flag, which means that entering the water is prohibited. We have become accustomed to associating this with cyanobacterial blooms. However, that is not always the actual reason. Bathing water quality is not only a matter of algal blooms, and the decision to allow bathing depends on more than just water quality.

The European Environment Agency report, or every coin has two sides

In mid-June, the European Environment Agency published its bathing water classification report. It was intended to be optimistic, as reflected in the figures: 96 percent of bathing sites met the quality criteria of the Bathing Water Directive, and 85 percent were classified as having excellent water quality. The press release was accompanied by a chart that caused considerable confusion in Poland. Our country ranked third from the bottom, with bathing sites of excellent quality accounting for only about half of those included in the summary. Does this mean that Polish bathing sites really have poor water quality and that this is why they are so often closed?

To understand the answer, one has to take a closer look at the European and therefore also the Polish system for monitoring and classifying bathing sites. The classification assigned to a bathing site does indeed depend on water quality, but the relationship is complex, and sometimes even a bathing site with a poor rating is not closed for that reason. This is because the classification is assigned only at the end of the bathing season. Moreover, it is based on several years of monitoring. A closer reading of the report reveals that Poland has an exceptionally high share of unclassified bathing sites, rather than bathing sites of insufficient quality. Many bathing sites were simply opened, either from scratch or after a break, less than four years ago and therefore cannot yet be classified.

State sanitary inspection and bathing water monitoring

The fact that a bathing site has not yet been classified for the purposes of the EEA report does not mean that its water quality is not being monitored on an ongoing basis. This is the responsibility of the State Sanitary Inspection. Although the monitoring is carried out by a public authority, it is not formally part of the State Environmental Monitoring programme run by the Environmental Protection Inspection. This may seem confusing, because the two authorities assess water quality according to completely different criteria that are unrelated to one another. A water body may have a very good ecological status while its water is unsuitable for bathing, and conversely, a bathing site with water suitable for bathing may fail to meet the criteria for very good ecological status.

The ongoing assessment carried out by the sanitary authorities is primarily intended to protect public health and focuses on factors that may affect people who accidentally swallow a small amount of water. For this reason, it does not include analyses of toxic substances in the long term, unlike drinking water quality assessments. The monitoring focuses on the presence of cyanobacteria (without identifying the exact species composition) and faecal bacteria: enterococci and Escherichia coli.

In Polish conditions, cyanobacteria from genera such as Microcystis, Aphanizomenon, Raphidiopsis and Nodularia (the latter in the Baltic Sea) are the main group of algae producing toxins that pose a risk to humans. Other toxic algae known from the Mediterranean, Australia, or the Gulf of Mexico have not yet appeared here. This is why the occurrence of a cyanobacterial bloom is treated as an indicator of danger.

An experienced observer can recognise such a bloom without microscopic analysis, and that alone is sufficient to justify the immediate closure of a bathing site. Since it is impossible to know whether a particular strain is producing toxins, the decision to close the site is made as a precaution without waiting for more detailed tests. The risk is simply too high. Moreover, even if a particular strain does not produce microcystins, nodularins or saxitoxins capable of causing serious poisoning, it often releases less dangerous but still irritating substances that may cause coughing or skin rashes.

Faecal bacteria do not appear as a visible bloom, so they must be detected and counted using microbiological methods. Although these bacteria are not necessarily dangerous in themselves, their presence indicates contamination with domestic sewage, which may contain more harmful microorganisms such as Salmonella. The higher their concentration, the greater the risk, so legal threshold values have been established. Once these are exceeded, the bathing site must be closed.

How often water quality is tested and where the results are published

The assumption is that bathing water is not contaminated, so the regulations require testing at least once a month. Whenever circumstances arise that raise concerns, the sanitary authorities do not wait for the scheduled date and immediately carry out additional testing. This happens, for example, after urban flooding, when domestic sewage may have entered the stormwater drainage system. The appearance of a bloom or any unusual discolouration of the water is also a signal for the monitoring authorities to take action. Once microbiological contamination or a cyanobacterial bloom has been detected, testing is carried out more frequently to determine whether the threat has passed.

The State Sanitary Inspection publishes the results of its tests on the bathing water website (https://sk.gis.gov.pl/ ). The website contains a list of 718 officially operating bathing sites in Poland during the current season. The easiest way to find them is on the map. Bathing sites currently open are marked with green pins, while closed bathing sites are marked with red pins. Clicking on a pin provides general information (the operator, the supervising district sanitary and epidemiological station, and infrastructure), as well as assessments from previous years and the current status. If the pin is red, the reason for the closure is also given.

Closed bathing sites and safety beyond sanitary issues

A green pin is not always a guarantee that a bathing site is open. It may happen that the sanitary authorities allow bathing because the water meets the required standards, but the operator closes the site for other reasons. The cause may be a different type of hazard: strong winds, high waves or rip currents. In such cases, a red flag is also raised on the beach. Although this is not a decision of the sanitary authorities, the information is still shown on the bathing site page in the Chief Sanitary Inspectorate’s online service in the form of a red flag icon, although it only becomes visible after clicking on the green pin.

In exceptional situations, a bathing site may even be temporarily closed for reasons such as the absence of an available lifeguard. It should be remembered that the regulations resulting from EU and national legislation are strict, and safety is the overriding principle, even if bathers sometimes see them as excessive caution. At the same time, operators, usually municipal authorities, sometimes regard these requirements as an excessive bureaucratic burden. This is one reason for the popularity of a solution that lies between a formally designated bathing site and a wild swimming area: a site occasionally used for bathing. Nevertheless, the number of bathing sites designated in accordance with the Bathing Water Directive has been increasing in recent years, probably along with growing awareness that this status provides a guarantee of quality and safety. No one closes a wild swimming area because of cyanobacteria, strong winds or the illness of a lifeguard, but no one is responsible for the safety of its users either.

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