There are a number of disease-causing bugs (called pathogens) that once discharged into the marine and freshwater environments can survive for some time. These bugs mainly get into the water through human and animal faeces. Human and animal faeces can get into the water from many different sources. Every time we come into contact with water that has been contaminated with human and animal faeces, we expose ourselves to these bugs and risk getting sick.
What are pathogens?
Pathogens are microscopic organisms that cause disease in humans and animals. There are many different kinds of pathogens. Some of the more widely known are Campylobacter, Salmonella, Giardia, Cryptosporidium and viruses that cause diarrhoea and cold and flu-like symptoms. These pathogens are present in faeces and may enter our waterways through untreated sewage discharges, leaky sewerage pipes, septic tanks, stormwater, rural run-off and from birds.
How high is the risk of getting sick in ‘clean’ water?
The maximum acceptable level of risk for marine waters has been set at 19 in every 1000 bathers contracting an illness. For freshwaters, the accepted level of risk has been set at 8 in every 1000 bathers contracting an illness. These levels used by Environment Canterbury are based on overseas guidelines which have been confirmed by New Zealand studies.
This means that, even when beaches, lakes and rivers meet the guidelines, there will still be a slight health risk when you swim at that spot. Because scientists are not directly measuring the pathogens, it is not possible to say there is zero risk to public health, especially where there are known sources of human and animal faeces near the water.
If tested waters exceed the acceptable level of risk, the public is advised that the area is unsuitable for recreational activities in the water.
What illnesses can you contract from swimming in contaminated water?
Illnesses related to contact with recreational waters were initially thought to be confined to gastrointestinal illness such as salmonellosis, Giardia and Campylobacter. These pathogens cause diarrhoea and sometimes vomiting associated with ‘tummy bug’ symptoms. Recent studies indicate that you can also contract respiratory illnesses, such as those that cause cold and flu-like symptoms, from swimming in contaminated water. Skin, eye and ear infections can also be caught through contact with contaminated marine and fresh waters.