Waiau River gorge, Hanmer Springs, Canterbury. Photo: 123RF
Almost a quarter of swimming spots in Canterbury's rivers, lakes, bays and streams aren't safe for swimming, paddling or playing in, according to data released by the regional council.
The result, which showed no change from the previous year, came from monitoring 52 freshwater and 47 coastal sites last summer.
Graded for risk
The sites were graded on suitability for recreation, based on enterococci (freshwater) and E. coli (coastal water) bacteria levels that indicated faecal contamination.
The grades were an indicator of risk, rather than a firm no-go, acting council chief scientist Dr Elaine Moriarty said.
"They never say to go or not to go," she said. "It's what's the risk attached and the public makes that decision, depending on if you're fit and healthy, if you're going through medical treatment, or you're an older person and prefer not to."
Canterbury Medical Officer of Health Dr Cheryl Brunton said high bacteria levels could cause gastroenteritis, ear, eye, nasal cavity, skin and upper respiratory tract infections.
Rivers 'more challenging'
Canterbury's coastal sites received an 85 percent pass - the same as 2023/24 and an improvement on 77 percent the year before - while 100 percent of open coast beaches passed.
Freshwater sites fared less well, with 71 percent suitable - 87 percent of lake sites and 64 percent of river sites.
Rivers were "more challenging, particularly in the lower reaches of urban and agricultural catchments", Moriarty said
Few changes
Two freshwater sites received improved grades:
- - Te Waihora/Lake Ellesmere at Lakeside Domain went from unsuitable to suitable, although it remained off limits, due to a permanent cyanobacteria warning
- - Waihī River at Gorge improved from fair to good
Six freshwater sites received lower grades - half of those dropped from suitable to unsuitable:
- - Pareora River at Evans Crossing, Temuka River/Te Umu Kaha at SH1 and Lake Alexandrina at Bottom Huts went from suitable to unsuitable
- - Ashley River/Rakahuri at SH1 and Ōrāri River at Gorge deteriorated from good to fair
- - Lake Hood at Baylis Beach deteriorated from very good to good
The freshwater sites that fared the worst (very poor) were:
- - Waiau Uwha River, upstream of SH70
- - Avon River/Ōtākaro at Kerrs Reach
- - Selwyn River/Waikirikiri at Upper Hutts
- - Ashburton River/Hakatere at SH1
- - Waihao River at Black Hole
Two estuary sites - Avon-Heathcote Estuary/Ihutai at Humphreys Drive and Ashley River/Rakahuri Estuary - were unsuitable, as were five Lyttelton Harbour Whakaraupō sites:
- - Corsair Bay/Motu-kauati-iti
- - Rāpaki Bay
- - Diamond Harbour Beach
- - Purau Beach
- - Governors Bay Sandy Beach
The Cass Bay boat ramp, Charteris Bay/Te Wharau at Paradise Beach and Church Bay all rated fair, the highest grade of any Lyttelton Harbour sites.
A multi-year investigation by the regional and city councils, Te Whatu Ora and iwi into Lyttelton harbour contamination was ongoing.
Testing, public education and Faecal Source Tracking had been undertaken, and several streams and stormwater outfalls were identified in this season's investigations, Moriarty said.
Legislative threats
Otago University researcher Marnie Prickett said more information about water trends would help the public understand if pollution was reducing or increasing.
Changes underway to wastewater standards and freshwater policy posed further threats to much-loved swimming spots, she warned.
"Canterbury is facing even worse pollution of swimming holes through dairy expansion and lower wastewater standards. The public needs to be aware that things could get worse, if regional councils... don't stand up to the short-termism of the current government."
E.coli in groundwater was also increasing. It was detected in 14 percent of samples in the most recent groundwater testing, up from nine percent the year before.
Moriarty said the council held detailed information on trends that could be made available, but she did not have data to hand on which way bacterial counts were heading within grades.
Public health warnings
Last summer, 46 temporary public health warnings were issued across 41 sites, including 28 warnings for faecal contamination and 18 for toxic algae.
Toxic algae (cyanobacteria) was "a naturally occurring algae" that could harm or kill dogs, people and other animals, the council's statement said.
Exposure can cause rashes, nausea, stomach cramps and numbness, and could result in seizures, liver and neurological damage.
Describing cyanobacteria as "naturally occurring" elided the reasons behind increasing cases, Prickett said.
"It's not OK or responsible for [the regional council] simply to emphasise toxic algae is 'naturally occurring', without adding human activities have dramatically increased how much toxic algae we find in our waterways. [The council] is responsible for managing those activities and should be more upfront about this."
Cyanobacteria can be exacerbated by nutrient runoff, including nitrogen and phosphorus, sediment and climate change.
Moriarty agreed that cyanobacteria was increasing, but said there were many drivers.
"It's a complex relationship. It's a reflection of the water quality, but it's also a reflection of the temperature. If we have a hot summer, we have a lot of still water... when that happens, the naturally occurring bacteria increase in numbers."
The report recommended permanent signs be erected to warn the public to stay out of the water at two dozen sites:
- - Lyell Creek/Waikōau Lagoon
- - Hurunui River at SH7
- - Waipara River at Boys Brigade Swimming Hole
- - Kaiapoi River at Boat Ramp
- - Avon River/Ōtākaro at Kerrs Reach
- - Avon River/Ōtākaro at Margaret Mahy Playground
- - Avon River/Ōtākaro at Fendalton Road
- - Heathcote River/Ōpāwaho at Catherine Street
- - Ōtūkaikino Creek at Swimming Hole
- - Waimakariri River upstream of the old Highway Bridge
- - Waimakariri River downstream of SH1
- - Selwyn River/Waikirikiri at Coes Ford
- - Selwyn River/Waikirikiri at Upper Huts
- - Waimakariri River at Thompsons Road
- - Ashburton River/Hakatere at SH1
- - Temuka River/Te Umu Kaha at SH1
- - Lake Alexandrina at the bottom huts
- - Lake Opuha at Ewarts Corner Boat ramp
- - Pareora River at Evans Crossing
- - Pareora River at Huts
- - Waihao River at Black Hole
- - Ashley River/Rakahuri Estuary
- - Avon-Heathcote Estuary/Ihutai at Humphreys Drive
- - Governors Bay at Sandy Beach
New model to provide real-time data
The council unveiled a new predictive water-quality model for some sites in Lyttelton Whakaraupō and Akaroa harbours, which it anticipated would be ready this summer.
The current system meant sites could be considered unsuitable all season, based on five years of data, which had caused "frustration in the past", Moriarty said.
The new model used real-time information, including rainfall, wind direction and tides, combined with historical data to predict water quality.
Similar systems operated in Auckland, Northland and Wellington, and meant people could make decisions based on current conditions, she said.
"Instead of blanket unsafe warnings that might last for days or even the whole summer, people will get information that responds to changing conditions."
The model would not replace physical water sampling.
Swimming should be avoided for 48 hours after rain, which can wash bacteria into waterways, and people should always check the Land Air Water Aotearoa 'Can I Swim Here?' website.
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