Community and Public Health (a division of Canterbury District Health Board) has issued a health warning for swimming for at least 48 hours after heavy rainfall - more than 10mm rainfall over a 24 hour period.
Canterbury Medical Officer of Health Dr Alistair Humphrey says "rainfall in the Canterbury region in the last week from ex-Cyclone Gita is likely to cause many swimming spots to pose an increased risk of infection."
Water can be contaminated during heavy rainfall from surface water runoff, overloaded septic systems, sewage overflows and backflow, rural runoff and sediment.
Water contaminated by human or animal faecal bacteria may contain a range of disease causing micro-organisms such as viruses, bacteria and protozoa.
"In most cases the ill-health effects from exposure to contaminated water are minor and short-lived. However there is the potential for more serious diseases such as hepatitis A, giardia, cryptosporosis, campylobacter and salmonella," Dr Humphrey says.
Environment Canterbury routinely sample sites for microbiological suitability for swimming however it is also important to note that the test results are only a snapshot of conditions at the time of testing, and if there has been heavy rain since, it's likely the water quality will be worse.
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