Poor microbiological quality of surface water such as lakes, rivers and canals used for recreational purposes by large groups of people may lead to many cases of disease. Microbiological contamination can originate from various sources, including both human and animal faeces, but can also result from increased levels of naturally occurring microorganisms. In Europe, the European Bathing Water Directive applies to all official bathing sites. At these locations, water quality must be checked regularly and must meet requirements for maximum faecal contamination. However, the most common recreational water-related health conditions in the Netherlands are skin complaints, predominantly 'swimmers itch'; this is caused by Trichobilharzia, a parasite of non-faecal origin. The number of disease outbreaks in any summer is strongly linked to the number of days when the maximum temperature is 25°C (77°F ) or above. Besides the impact of climate on recreational water-related pathogens, human behaviour also plays a role; the outcome of the interaction between these and other factors is as yet uncertain.