GE-I-5: Contamination of bathing waters with cyanobacteria – case study

The picture shows a boat paddle immersed in water with strong blue-green algae development.Click to enlarge
Bathing in waters contaminated with cyanobacteria presents health risks.
Source: Photograph: © Ingrid Chorus / Umweltbundesamt

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

GE-I-5: Contamination of recreational bathing waters with cyanobacteria – case study

Subject to weather conditions during the bathing season, health risks can develop in bathing waters owing to high concentrations of cyanobacteria. Surveys of the Müggelsee in Berlin have shown that a major reduction in nutrient inputs from the end of the 1980s resulted in a marked decrease in contaminations.

The line graph represents the average biovolume of cyanobacteria (July to September) and the total phosphorus content (July to September) since 1979. The biovolume decreases significantly with large fluctuations between years. The total phosphorus content decreases with a quadratic trend also with strong fluctuations.
GE-I-5: Contamination of recreational bathing waters with cyanobacteria – case study

The line graph represents the average biovolume of cyanobacteria (July to September) and the total phosphorus content (July to September) since 1979. The biovolume decreases significantly with large fluctuations between years. The total phosphorus content decreases with a quadratic trend also with strong fluctuations.

Source: Leibniz-Institut für Gewässerökologie und Binnenfischerei IGB (lake monitoring)
 

Cyanobacteria – impairment of recreational bathing waters

If temperatures rise in future summers, the desire of humans for a cooling bath in lakes or rivers and the sea will increase. At the same time however, climate change can affect the quality of recreational bathing waters. A much discussed health risk in connection with climate change is the contamination of recreational waters with cyanobacteria, commonly known as blue-green algae.

Increased concentrations of blue-green algae occur particularly in waters which are rich in plant nutrients, especially total phosphorus. In waters only moderately contaminated with nutrients, cyanobacteria have to compete for available nutrients with both higher water plants and with other phytoplankton, thus rarely achieving dominance. However, if there is heavy contamination with nutrients, this often results in mass reproduction of cyanobacteria, so-called ‘algal bloom’. This is exacerbated by stable thermal layering of waters which develops especially at high temperatures and stable weather conditions. Stable layering also leads to the deposition of some cyanobacteria at the surface thus potentially resulting in further localised accumulations of cyanobacteria. In view of increased algal bloom owing to weather conditions, the possibility of a relationship between climate change, water warming and health impairments caused by cyanobacteria is discussed.

It has been observed that bathing in waters heavily contaminated with blue-green algae has led increasingly not only to symptoms such as irritations of the skin and mucous-membranes as well as allergic reactions, but also stomach, intestinal and respiratory illnesses. Whether these are ultimately caused by toxic cyanobacterial substances (cyanotoxins) or by accompanying bacteria has not yet been clarified. The absorption of major quantities of cyanotoxins can lead to serious impairment of the liver, kidneys and nerves. The risk is particularly high for young children and children at primary-school age who are apt to swallow unintentionally large amounts of water while crawling about or frollicking in shallow water. The same risk factor applies to inexperienced water sportsmen or women who do not just swallow water but also absorb it into their respiratory system when surfing or water-skiing in water contaminated with cyanobacteria.

If water looks distinctly turbid owing to the presence of cyanobacteria or especially if there are streaks forming on the surface, it is advised not to enter the water for bathing. The same precautions should be taken for dogs.

Observations have shown that the relationships in the course of contamination with cyanobacteria are complex; any generalisations would therefore be fraught with extraordinary problems. Depending on nutrient availability, size, depth, wind exposure and type of water use, the development in different waters can differ a great deal. In order to be able to make statements that apply nationwide, it would be necessary to carry out more observations of waters used for recreational bathing. It must be said, however, that currently research into the occurrence of blue-green algae in waters varies considerably. In view of the currently available data, it is not possible at present to make any statements regarding the question whether in recent years there has generally been an increase in contamination with blue-green algae of recreational bathing water in Germany.

Nevertheless, the data on developments in the Große Müggelsee lake over the past almost forty years can serve as an example. This largest of the lakes around Berlin has considerable recreational value, especially for the eastern parts of the city. The biomass of blue-green algae has decreased since the 1980s. The marked decrease from the end of the 1980s until the beginning of the 1990s is primarily due to the reduced input of nutrients via the Spree river after German unification in 1989. Since the mid-1990s, however, there have been no discernible trends, for contamination either with phosphorus or with blue-green algae biomass. This is due in part to the fact that contamination with phosphorus is still exceeding the critical threshold above which blue-green algal bloom can develop. Besides, rising temperatures repeatedly cause extended periods of more stable layering in water bodies. These layerings are particularly apt to favour the development of cyanobacteria which in those phases can also produce very high proportions of the total phytoplankton biomass.

The sometimes remarkable fluctuations of contamination with cyanobacteria between years are essentially due to variations in the layering events which occurred in those years. For example, in the hot summer of 2003 the layering was less stable than in summer 2006 – a year in which comparatively high amounts of cyanobacteria biomass and a cyanobacteria content of 80% were measured in the phytoplankton biomass. A more frequent occurrence of stable layerings may in future counteract the positive effects of reduced nutrient inputs on contamination with cyanobactera, provided the nutrient concentration in the water is not at levels that would clearly limit the growth of cyanobacteria (<30 µg total phosphate per litre).

 

Interfaces

WW-I-6: Start of the spring algal bloom in standing waters

 

Objectives

In cases of mass reproduction of cyanobacteria and health risks, appropriate management actions to be taken without delay in order to prevent exposure to these risks. In addition, information to be disseminated among the public (EU Bathing Water Directive, Art. 8).