A child plays in Whanganui's Mowhanau Stream, despite warning signs. Photo / Stuart Munro
A child plays in Whanganui's Mowhanau Stream, despite warning signs. Photo / Stuart Munro
Swimmers are being warned to keep clear of three Whanganui streams - places that are especially popular with young children.
Warning signs went up at the Mowhanau and Kai Iwi streams at Kai Iwi Beach on January 18, and Ototoka Stream, further north, was deemed unfit for swimming on January 11.
The streams were given "special status" because their poor or highly variable water quality made them unsuitable for swimming, Horizons Regional Council science manager Abby Matthews said.
"Because the results have been consistently poor this season, we've made a decision to put permanent warning signage in place for now."
Mowhanau Stream has high levels of E. coli, nitrogen and phosphorous.
E. coli is an indicator of contamination from the faeces of warm-blooded animals, including humans, birds and stock. It's usually not a problem in itself, but indicates other disease organisms may be present.
The risk of getting ill depends on the degree of contamination, and that varies over time.
Whanganui Medical Officer of Health Patrick O'Connor said the most likely illnesses from contaminated water are viral. People swallowing the water can get gastroenteritis - diarrhoea and vomiting - and people inhaling it can get acute febrile respiratory illness - a brief fever and cough.
Usually those illnesses will kick in within 24 hours, and people are not obliged to notify them to health authorities.
"I can't provide you with cases of people that have actually got sick. Even if they did, it's very hard to pinpoint the actual source," Dr O'Connor said.
Despite any evidence of real risk, the warning signs are worthwhile, he said.
"I don't think it's alarmist. It's giving people the best information that we have. We've got to share that information. Clearly people will make their own decisions as a result of that."
He said there could be other coastal streams affected.
"They don't obviously monitor every coastal site. There may well be more widespread problems."
A contractor to Horizons Regional Council takes samples at Mowhanau Stream. Photo / Stuart Munro
Horizons monitors more than 80 swim spots weekly during the summer months. On Thursday there was a contractor taking monthly water samples in the Mowhanau Stream.
"Being quite small streams they're really susceptible to things like run-off from farming and, during the summer period, leakage from septic systems," Ms Matthews said.
Not much water was running through, and warm conditions were ideal for bacteria to grow.
The council has been working to improve the stream for years, with iwi support, fencing, and planting.
Last year it seemed to be improving, but this year's results have been "quite poor". More testing will be done, to find what sort of faeces are present.
Farming, even non-intensive farming, and human settlement all have big impacts on coastal streams, Ms Matthews said.
"If I had a choice between swimming in a coastal stream next to a beach, or swimming at the beach, I would always choose the beach."
