Green water and mud on the coast: What's happening in Slovenia's natural bathing areas?

In recent weeks, natural swimming pools along the Slovenian coast have been experiencing unusual changes in water quality, raising concerns among visitors and local authorities alike. The phenomenon has been observed on several locations, including Šobčev Bajer near Maribor and coastal areas such as Pod Turistiko, Debeli Rtič, and near the Hotel Piran. These changes include a noticeable greenish tint in the water and the presence of algae and slime on the surface. While these developments are not necessarily dangerous, they have prompted warnings about potential skin irritation and increased slipperiness on rocks.

The Agency for Environment of the Republic of Slovenia reported that after sampling on June 29, a significant change in the color of the water was detected in Šobčev Bajer. The transparency of the water had decreased, and the analysis revealed that this was due to reduced water flow through the pool combined with high temperatures. This led to an increase in biomass of planktonic algae, giving the water its characteristic greenish hue. The examination of phytoplankton showed that two types of algae were particularly prevalent: the golden alga Dinobryon sp. and diatom algae from the genus Fragilaria.

These findings highlight how environmental conditions can influence the biological composition of natural water bodies. High temperatures and low water flow create ideal conditions for the proliferation of certain algae species. While most of these algae are not harmful, their presence can lead to discomfort for swimmers, especially those with sensitive skin. The National Institute of Public Health (NIJZ) has issued guidelines to help mitigate risks associated with these changes. They recommend that swimmers avoid drinking the water, rinse off thoroughly after swimming, and keep young children and pets away from areas where algae have accumulated on the surface.

Similar issues have also been noted in coastal waters. On June 29, three locations along the coastline—Pod Turistiko, Debeli Rtič, and near Hotel Piran—were found to have deposits of sea grass covered in layers of slime. NIJZ has advised swimmers to temporarily avoid these areas until further notice. Despite these observations, the microbiological quality of all Slovenian swimming waters remains within acceptable limits according to current standards. This indicates that while the physical appearance of the water may have changed, there is no immediate health risk posed by microbial contamination.

The situation reflects broader environmental trends affecting natural water systems globally. Rising temperatures and altered hydrological patterns contribute to shifts in aquatic ecosystems. In Slovenia, these changes are being closely monitored by environmental agencies and public health officials who are working to ensure that recreational activities remain safe for the public. Their efforts involve regular testing of water samples and issuing timely updates to inform the community about any potential hazards.

Local authorities and environmental experts are collaborating to understand the long-term implications of these changes. They are examining whether climate-related factors are playing a role in the increased growth of algae and other organisms in natural swimming areas. Additionally, they are exploring ways to manage water flow and temperature more effectively to prevent similar occurrences in the future. This includes evaluating infrastructure improvements and implementing measures to maintain optimal water conditions for both ecological balance and human use.

As the summer season progresses, continued monitoring will be essential to track any further developments. Authorities are prepared to take additional precautions if necessary, ensuring that the enjoyment of natural swimming areas does not come at the expense of public safety. For now, swimmers are encouraged to follow official guidelines and stay informed about the status of their preferred swimming spots.