Critically endangered birds that nest along the Ashburton River are making it unswimmable for people.
The river has long been rated as polluted, but ongoing testing for the source of the ecoli contamination points to precious birds like the black-billed gulls who feed, wade and poo in it.
The river has been a waterway of concern for the Ashburton Water Zone Committee, who commissioned investigation after investigation as the finger was pointed at farmers for polluting practices.
But the birds are to blame.
Principal surface water scientist Adrian Meredith said there was no longer any point in further investigations as work over the past 20 years provided strong evidence that high ecoli levels in the river came from an avian source.
Prior to the past week’s wet weather, some 8000 endangered black-billed gulls were nesting in the river about 1.5km upstream of the State Highway 1 bridge.
Thousands of black-backed gulls are also known to frequent the area.
Water sampled at SH1 in summer and autumn reflected their presence through faecal source tracking technology, Meredith said.
The ecoli readings did not correlate to river flow variations.
It was likely the contamination pattern had been occurring in the river for a long time but only became an issue when regular water quality sampling began, he said.
Environment Canterbury will continue to sample the water as part of its regular monitoring programme but the water zone committee said investigations into the source could stop.
Meredith said because the riverbed birds polluting the river were highly valued and endangered, controlling the source was not an option.
Swimmers needed to be redirected.
While the birds were generating more than 50 per cent of ecoli in the river, it was still important to reduce other known sources, like livestock, he said.
Meredith said SH1 was a convenient spot for swimmers, but the committee could consider enhancing a swimming hole in the river that was less affected by the birds.
Committee member Angela Cushnie said the river’s poor water quality rating had been used to discredit rural people.
Stuart Wilson agreed.
“It is a pity we can’t publicise nationally it is unsafe to swim at State Highway One because of endangered bird species.
“It (the river) always gets a red cross because it is highly contaminated.
“It is not giving everyone outside the district a fair image.”
Meredith said a safe swimming spot might be found on the north branch as it was less contaminated.
Endangered birds nesting in the riverbed near Lake Hood are also to receive a helping hand with their survival.
A gate and signage is to be erected on an access road to the riverbed to keep vehicles out and stop them running over nests in and along the riverbed.
It is an offence under the Wildlife Act to disturb endangered, nesting birds and punishable by a maximum $20,000 fine.
– By Linda Clarke