Vibrio ions in almost all samples: New investigation in the Baltic Sea and Schlei
YACHT
· 31.05.2026
The Schleswig-Holstein Ministry of Health had water samples from 36 bathing waters along the Baltic Sea coast and in the Schlei analysed in 2025. The bacteria were detected across the board, but the concentrations were mostly within the expected range. However, this can pose a risk for water sports enthusiasts with pre-existing conditions.
The aim of the investigation was to obtain up-to-date information on the occurrence of vibrios. According to the Mecklenburg-Vorpommern State Office for Health and Social Affairs, vibrios were detected in all 72 samples - the coasts of Schleswig-Holstein and Poland were also affected. However, there is no cause for concern for most bathers and water sports enthusiasts. Vibrio infections are dangerous, but very rare. However, risk groups should be careful.
Widespread distribution - low concentrations
One sample was taken in July and one in August from 36 bathing waters that were geographically evenly distributed along the Baltic Sea coast - including the Schlei, excluding Fehmarn. The samples were analysed for the three potentially human pathogenic vibrio species Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio cholerae.
The results are almost entirely within the range of expected or slightly elevated concentrations (1 to 100 CFU/ml). In the total of 72 samples, an increased concentration of vibrios (over 100 CFU/ml) was found in only two samples. CFU stands for colony-forming units - a measure of bacterial density in water.
Vibrions were found more frequently and in higher concentrations in the Schlei than in the Kiel Fjord. In the outer Schlei, Vibrio parahaemolyticus was mainly detected, in the middle part of the Schlei there were more findings of Vibrio vulnificus, while in the inner Schlei Vibrio cholerae was mainly detected. The distribution of species is therefore dependent on the conductivity - and therefore the salinity - of the water.
What makes vibrios dangerous
Four potentially harmful non-cholera vibrios are found in the Baltic Sea and nearby brackish waters such as the Schlei or Kiel Fjord: Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio cholerae non-O1/non-O139. Vibrio bacteria are part of the natural bacterial flora of the Baltic Sea. They are comma-shaped and do not tolerate much salt: a maximum of around 2.5 per cent.
If the temperatures of salty seawater and brackish water rise to 20 degrees and above in the summer months, the conditions are ideal for the rod-shaped bacteria to spread. Even if the water temperatures fall below 20 degrees again, the bacterial density in the affected waters can remain high for weeks.
The pathogens can pose a health risk to bathers if they enter the body through skin injuries. They enter the human organism via injuries to the skin - a bloody mosquito bite can be enough.
Risk groups particularly at risk
Immunocompromised and chronically ill people have a significantly increased risk of severe disease progression. The bacteria are particularly dangerous for the elderly and immunocompromised people. People with pre-existing conditions such as diabetes mellitus, liver disease, cancer and severe heart disease also have an increased risk of becoming infected and falling seriously ill.
Since 2003, a total of 95 infections have been reported in Mecklenburg-Vorpommern, 14 people have died, 13 of whom had relevant pre-existing conditions. The cases occurred mainly in the warmer summers of 2003, 2006, 2010, 2018 and 2019. Since reporting became mandatory, the number of cases to date has ranged between 13 (2020) and 53 (2022).
Take symptoms seriously
One noticeable symptom is unusually severe pain, even with small wounds. In such cases, a doctor should be consulted quickly. If your skin becomes increasingly reddened after swimming in the Baltic Sea, you should consult a doctor immediately.
In healthy people, a Vibrio infection can be easily controlled if recognised early. In most cases, the infection can be quickly brought under control with antibiotics.
Tips for water sports enthusiasts
It is recommended to use a waterproof plaster for small open wounds. Waterproof plasters are available everywhere. Doctors also advise people who have had an operation to avoid swimming in contaminated water for a fortnight.
People with chronic illnesses and large open wounds are advised to avoid swimming or wading in the Baltic Sea. It is also recommended that seafood should not be eaten raw. Bathing bans due to the risk of vibriosis are not considered sensible, as the bacteria are found everywhere. There is also no threshold value above which an infection is likely.
Very low risk
Vibrio infections currently pose a very low risk to healthy people. Compared to the most common causes of death, such as cardiovascular diseases and cancer, as well as road accidents and suicides, the risk from vibrio infections is negligible.
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