RIVM has identified the micro-organisms that can make people sick by contact with bathing water and to what extent climate change might have an influence on that risk. Climate factors, such as temperature, UV radiation and precipitation, influence the physiology of pathogens. These climate change factors can cause pathogens to die faster, survive longer, or proliferate more rapidly. This will affect the chance that pathogens will cause diseases when people come into contact with bathing water.

The expectation is that increased water temperatures will lead to higher numbers of some pathogens present in bathing water. That stronger pathogen presence could lead to more people falling ill. There are a number of bacteria that are naturally present in bathing water and can multiply there; two examples are Vibrio (can cause ear infections and infected wounds) and Pseudomonas aeruginosa (can cause ear infections as well). Increased UV radiation and the accompanying rise in temperature can cause pathogens to proliferate more rapidly – or die off due to DNA damage. Heavy rainfall may cause a huge spike in micro-organisms from faeces that temporarily end up in local bodies of water. Such contamination may occur, for instance, when the sewage system floods due to high volumes of rainwater, or when manure used as fertiliser is washed off the land and ends up in bathing water.

Climate change is one of the many factors that affect the extent to which pathogens are present in water. The impact of climate change compared to other relevant factors is not yet clear. More research is required to determine how climate change affects new and known pathogens that are transmitted by contact with bathing water. Topics for further research include the influence of climate change on pathogens and on how people approach swimming in surface water.