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A colony of nesting gulls responsible for polluting the Kakanui River and a popular North Otago swimming hole cannot be removed from the area because the colony contains protected bird life.
The Otago Regional Council located a previously unknown gull colony on steep rocky faces, 5km above Clifton Falls in February, after an investigation was launched to examine the cause of a series of high E. coli levels recorded in the river.
Council resource science manager Matt Hickey said an aerial inspection of the site had revealed that the colony contained at least one species of protected gull, and that meant the council could not act to remove the nesting birds.
''There are three species of gulls, and two of them are protected.
''Basically it's just one of those things, native birds doing what they do, and we can't really do much about it, other than a few signs warning people at that swimming hole during December-January that there are colonies upstream breeding.''
E. coli levels at Clifton Falls breached safety guideline four times last summer and peaked at 2400 parts per 100ml of water on January 3, well above the council's limit of 300 parts per 100ml.
Although Government water-quality guidelines for recreational swimming areas suggested that those with E. coli concentrations of more than 550 parts per 100ml could pose a health risk, Mr Hickey said there had been no reports of any illness suffered as a result of swimming at Clifton Falls.
However, warning signs would be put in place in time for next summer, he said.
''Those colonies have probably been there for at least 20 years, probably longer. But it's good to know that there is a risk and people can make their own judgement when they go swimming, whether they want to take that risk or not.''