A wide variety of human diseases are caused by waterborne pathogens originating from the faeces of humans or mammals. These include campylobacter, salmonella, typhoid, cholera and Hepatitis A. These pathogens are microscopic living organisms from faeces which are invisible to the human eye when in water, but can be identified and counted in a laboratory for a water test.
Swimming and other high-contact water sports in waters contaminated with faeces creates a reasonable risk that water will be swallowed, inhaled, or make contact with ears, nostrils, and cuts in the skin, allowing the pathogens to enter the body.
Gastroenteritis is the most frequent (ie, diarrhoea, vomiting, and gut pain), and respiratory illness is also common.
The guidelines used by Auckland Council for swimming alerts for our coastal beaches are designed to keep illness among recreational water users to below 2 per cent, that is, up to two in 100 swimmers on average will become ill as a result of swimming at beaches when there are no beach closure notices.
Clearly, people who choose to swim when beaches are closed have a higher chance of getting sick. The size of this risk will depend on the amount of sewage pollution present.
For example, those brave enough to swim at any of the 16 permanently blacklisted swimming spots around Auckland reportedly have a 1 in 10 chance of gastrointestinal illnesses as well as a greater than 4 per cent chance of respiratory tract infections, such as coughs and colds.
Swimmable freshwaters in Auckland region have also been categorised for the health risks they pose to swimmers. More than 60 per cent of the length of Auckland's rivers are classed as poor, meaning that on average more than seven out of 100 swimmers will be infected. Auckland's lakes fare better, with two out of 100 swimmers predicted to become ill when swimming at over 90 per cent of lake margins.
People can choose to ignore the don't swim notices and the associated risks if they wish. Indeed, Mr Roughan admitted to going for a dip despite the health warning sign, although his grandkids were wisely kept out of the water, and potentially avoided a summer spoiler "gastro-bug" for his grandkids.
Admittedly the risks to people from ignoring the signs aren't clear to the public, nor is the council publically providing information on how much the sewage pollution tests for beaches are exceeding the threshold.
The best way to stop no-swimming signs going up at our beaches is to stop the sewage getting into the water in the first place. It has taken 40 years and we still aren't there yet, despite Auckland ratepayers spending billions on upgrading our wastewater systems. We rightly should be asking why.
Perhaps the failure to resolve this long-term problem has been the lack of awareness by Aucklanders of the extent of the sewage pollution on their beaches.
Hopefully the health warning notices that Mr Roughan finds so annoying, will finally spur the public and their council to move with a little more haste to finally fix the problem.
• Dr Andrew Jeffs is in the Institute of Marine Science at the University of Auckland.
