We carry out 12 weeks of sampling from early December to mid-February.
Tanya Gray, Environmental Recording Co-ordinator for the Northland Regional Council, says the region’s popular ‘bathing waters’ are generally suitable for swimming.
“But from time to time some do become contaminated with bacteria - particularly after heavy rain. Elevated levels of these bacteria indicate an increased risk of disease-causing pathogens which can make people sick.”
Mrs Gray says the Regional Council has been monitoring bacterial levels at popular swimming locations over summer since the late 1990s to gauge potential human health risks.
“Typically the Regional Council carries out 12 weeks of sampling from around early December to mid-February.”
She says hundreds of samples will be taken from popular coastal swimming spots including Tinopai, Pahi, Mangawhai, Ngunguru, Tutukaka Coast, Whangarei Heads, Bream Bay (including Ruakaka, Waipu and Langs Beaches), Oakura, Whananaki, Teal Bay, the Bay of Islands, Coopers Beach and Hokianga Harbour.”
A number of freshwater sites will also be monitored including Mangakahia, Kaikohe, the Kai Iwi Lakes, Otiria, Kerikeri, Waitangi, Tirohanga, Waipapa, Lake Ngatu, Kaihu, Lake Hikurangi, Whangarei Falls and the Raumanga Stream.
Test results – which will be posted weekly on the NRC’s website www.nrc.govt.nz - are forwarded to the relevant District Council and Northland Health.
Mrs Gray says it then becomes the responsibility of the three District Councils and Northland Health to follow up any elevated results. They may then decide on further investigations or public health warnings.
She says with several years of data now available, trends are starting to emerge.
“At open coastal locations, the health risks to swimmers are generally low, but the risk does increase in estuaries, harbours and freshwater sites after heavy rain and runoff, as contaminants tend to be more concentrated and may be present for several days”.
Mrs Gray says people should avoid swimming or gathering shellfish from such areas for several days after heavy rain.
“Another useful rule of thumb is that if the water is murky and you can’t see your feet when it’s knee deep, the water is likely to be contaminated and unsafe for swimming.”
She says coastal and freshwaters can be contaminated by variety of sources including sewage, septic tank seepage, discharges from boats, urban stormwater, run-off from farmland and stock in waterways.