Whangarei District Council is keeping an eye on black swans spotted at the city's drinking water reserve - the Whau Valley Dam - but say they are not a concern at this stage.
WDC water services manager Andrew Venmore said monitoring birdlife was part of the dam's process.
Several of the swans, which had infested some lakes in the Far North, had been spotted at the dam over the last week.
"We don't want nutrients from the droppings of large numbers of birds to increase quantities of algae, because that could make it more difficult and costly to produce the high-quality drinking water most of us are used to," Mr Venmore said.
"At this point there are very few birds on either (Whau Valley or Wilson's) dam."