Hunt on for contamination source
The Marlborough District Council has confirmed that a large slip on Department of Conservation land above the Spray River had affected the Craiglochart swimming hole in the Waihopai River.
The council posted warning notices at Craiglochart in late December and January after water testing picked up unsafe levels of bacteria from faeces. Farmers and others objected that there were fewer cows and sheep in the Waihopai Valley than 20 years ago so it was unlikely stock were the source of the pollution.
At a council environment committee meeting, monitoring officer Steffi Henkel showed photos of the slip, which spewed mud into the Spray River above its confluence with the Waihopai. Light killed bacteria in water, so high numbers had survived in the dirty water, she said.
Marlborough Mayor Alistair Sowman said the council must find the source of bacteria that affected swimming spots this summer so the problem could be fixed. Publicity about closed swimming spots at the height of the tourist season was embarrassing, he said.
Ms Henkel said the council was testing the DNA of bacteria from the Taylor and Opawa rivers in Blenheim and the Picton foreshore to find whether their source was animal or human.
The council erected warning signs at seven river swimming sites and three beaches through summer, mostly after heavy rain between Christmas and New Year and in mid-January, Ms Henkel said. However, high levels at the Blenheim river sites were not always timed around rain.
Council planning and development engineer Stuart Donaldson said sewage overflowed during heavy rain, typically near the foreshore.
Rainwater entered sewers at unauthorised stormwater connections and groundwater through cracks and joints in pipes.
"Every sewage system in the world has these problems," he said.
A $17.5 million upgrade of the Picton sewerage system should cut the frequency of overflows from just under three a year to one in five years, or one in 20 years at sensitive sites such as the Picton Marina, he said.
Work on the first stage of the project, upgrading the Picton harbour outfall, was finished in December, Mr Donaldson said.
Ms Henkel said run-off from intensive dairy farms was a likely source of faecal bacteria found at other Marlborough Sounds swimming sites, except Waikawa.
Rain also closed the Rai River, Rai Falls and Moetapu Bay for swimming, washing bacteria down the rivers to the beach, Ms Henkel said.
- The Marlborough Express