Towards the end of last year a report from the Otago Regional Council raised concerns about deteriorating water quality in the Kakanui River.
One of the contributing factors was an increased level of E.coli.
Dairying was blamed although the council couldn’t find the source.
One of the dairy farmers decided to do his own research and canoed down the river.
He found a couple of dead sheep caught in submerged branches then he came on a large colony of seagulls nesting in a canyon.
He reported this to the council which sent a helicopter up the river and found the source of the problem.
. . . a large colony of nesting gulls – was found in rugged terrain, about 5 km above the Clifton Falls bridge.
Water quality samples were taken immediately above and below the colony, with widely divergent results Upstream of the colony, the bacteria concentrations were 214 E.coli/100ml, whereas immediately downstream, the concentration was far greater at 1300 E.coli/100ml .
ORC manager of resource science Matt Hickey said that according to Government water quality guidelines for recreational swimming areas, those with less than 260 E.coli/100m should be safe, whereas water with more than 550 E.coli/100ml could pose a health-risk.
Mr Hickey said six colonies of gulls were found in total, on steep rocky faces, where they clearly favoured the habitat for nesting.
While they had gone undetected up until now due to the inaccessible nature of the gorge, it was likely the gulls returned each year to breed in the same places.
“Unfortunately, these nesting gull colonies are likely to continue to cause high E.coli concentrations in the upper Kakanui River, particularly during the breeding season,” Mr Hickey said.
“Bird activity, river flow, or even whether it is a cloudy or sunny day, (as E.coli often died quickly in clear water when exposed to sunlight) will influence actual bacteria numbers at Clifton Falls bridge. With hindsight, it reflects the random nature of the historical bacteria results at this site.”
Mr Hickey said the E.coli concentrations reflected a large number of birds congregating in a small area and we are fortunate this situation was not common in Otago. Historically E.coli concentrations in the lower Kakanui River have been very low, despite the gull colonies being found upstream.
The council is warning people against swimming in the river but we’ve had no warning about drinking the water, presumably because it’s treated.
Locals are very keen to solve the problem but it’s not necessarily a simple matter:
Coastal Otago biodiversity programme manager David Agnew said the Department of Conservation would look into the situation and try to identify which species of gull were nesting in the area.
Mr Agnew said the species involved would determine what could be done to remove them.
”Black-backed gulls are not protected so that’s not a problem as far as if they are causing a problem. They are not rare or threatened, they are not even protected, whereas red-billed gulls and black-billed gulls both have their own conservation concerns.”
There’s no concern about conservation with cows. If they were causing water quality problems farmers could face prosecution and would have to act quickly to address the cause.
Some gulls have a special status and if they’re the ones fouling the water the clean up will take some time.