More Sleuthing Planned To Track E.Coli In Westport Lagoon

Wednesday, 8 October 2025, 5:08 pm
Article: Lois Williams - Local Democracy Reporter

West Coast Regional Council science staff plan to carry out further sleuthing, to track down the source of human E.coli bacteria in Westport’s Orowaiti Lagoon -- and septic tanks are in their sights. 

Recent water sampling was done after concerns were raised by mana whenua, the Buller District Council and the community. 

Results showed contamination in the lagoon from farm run-off, birds and human septic waste, the council’s Resource Management committee heard yesterday. 

The Orowaiti river is popular with whitebaiters. 

The Lagoon has a long history of high E. coli levels, with data dating back to the late 1990’s, science staff reported. 

“The Buller District Council monitors sewage overflows into the Orowaiti Lagoon - [but] no overflows were recorded prior to any of these sampling events. Septic tanks could be contributing to the human E.coli contamination observed.” 

BDC was working to reduce infrequent sewage overflows into the Lagoon, removing private stormwater and sewerage cross-connections, the report said. 

“Given the lack of overflows when human contamination was detected, the WCRC science team are working to consider closer evaluation of septic tanks in the catchment as a potential source of human E.coli in the lagoon.” 

Buller councillor Chris Coll asked where the samples had been taken - and suggested working upstream might pinpoint the source. WCRC environmental manager Shanti Morgan told LDR the levels of human E. Coli were relatively low, and no norovirus had shown up in shellfish, which was a good sign. 

“But even a small amount can be a health risk, so our next step will be looking at any septic tanks in the area that could be responsible, doing some mapping and carrying out compliance work,” she said.

Faecal contamination from agriculture in heavy rain was still a difficult issue, but the WCRC catchment coordination team was working with the Kawatiri catchment collective to find solutions where run-off was a contributing factor, the report said. 

Over the past six months, the council’s Environmental Quality team had been working throughout the region, collecting data about the health of estuaries, including Cobden’s Aromahana lagoon, Okarito, Karamea, Okuru and Blaketown, the report said. 

Sediment tested for heavy metals, hydrocarbons and DDT showed very low levels and a low risk of negative ecological effects. 

“The study was the first detailed assessment for most of these estuaries. We’ve received lab results for all sites except Blaketown Lagoon. 

"So far, all potential contaminants have been below default guideline values…. DDT and petroleum hydrocarbons were below detection levels," the report found. 

-LDR is local body journalism co-funded by RNZ and NZ On Air.

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