Warning signs go up at Horowhenua waterways after heavy rain

Health risk warning sign up at an entry point into the Ohau River at the Kimberley Reserve this month.

Sewage overflows are creating a stinky situation for many New Zealand beaches as sewerage systems fail to cope with heavy rainfall.

In total, more than 100 beaches, rivers and streams in New Zealand currently have cautionary notices in place for swimming, according to the Land, Air, Water Aotearoa (LAWA) website, with about 60 of those deemed unsuitable for swimming.

Horizons Regional Council is reporting 22 areas to avoid swimming at, and nine others with potential health risks.

Safeswim technical leader Dr Martin Neale said some of the warnings were due to heavy rain washing contamination from land into the ocean, but others were triggered by wastewater overflows.

However, the latest available data from Horizons on testing for faecal indicator bacteria relates to February 4, almost a week before the weekend's heavy rainfall.

Sites currently flagged as red in Horowhenua include Wairarawa stream at Waitarere Beach, Mangaore Stream, downstream from Mangahao Power Station, Ohau River at SH1 Ohau, and at Kimberley Reserve, and also Lake Horowhenua at the domain.

There are cautions in place for Hokio Estuary at Muaupoko St bridge, and Ohau River at Kirkaldies Reserve.

Horizons Regional Council science and innovation manager Abby Matthews said the data is updated following an independent accredited laboratory testing samples taken at each of the 80 swim spots on a weekly basis. "We test for bacteria — E. coli and cyanobateria for freshwater sites such as rivers and lakes and Enteroccoi for coastal beaches.

"As this testing takes approximately 48 hours to process, we are unable to update bacteria levels until the following week.

"We do instead including messages both online and at each swim spot that recommends avoiding swimming following rain."

National guidelines for bacteria determine when intervention is required.

In beach samples, if more than 280 enterococci are detected in 100ml of water, a public warning is required to be issued.

Respectively, in river samples, if more than 550 E. coli are present in 100ml of water then warnings are also required.

The most common illness caused by the bacteria is gastroenteritis but respiratory illness and ear and skin infections may also occur.

Council websites recommend not swimming at beaches or rivers for 48 hours following rainfall due to overland runoff — even if a site generally has good water quality.

Shellfish should also not be taken within that period as they may exceed maximum microbiological guideline levels.

The results from water monitoring, including any current water quality warnings, can be found on individual council websites or on the Land, Air, Water Aotearoa (LAWA) website www.lawa.org.nz